Oh this is bad. I wish I had read this sooner! I've been pacing back and forth and wanting to hit something reading this story unfold.
I'll be keeping you and yours in prayer, for sure, and I might even be able to offer some assistance. I've been where your daughter is... actually I'm still there sometimes so I could use your prayers as well

. I'm going to give a brief background on myself to show you where I'm coming from, and please for heaven's sake share this story with your daughter, it might save her a
LOT of pain and suffering. If the mods think I'm out of line in any of this post, please let me know and I'll edit it. Meanwhile I'm going to just get this over with as I'm really nervous writing it.
I'm not that much older than your daughter... less than a decade. I went through some seriously confusing and hard times and made the mistake of not learning from them and opening old doors recently. I'm still fighting to get those freaking doors slammed shut, and frankly I've been hoping God would give me a chance to fight against the darkness that has tortured me. Maybe he's giving me that chance now by telling this story.
When I was in high school, I got really sick (it's actually taken YEARS to get over it too and it got worse recently with those stubborn doors - which was dumb of me because it was much better before the doors). Suffice it to say that should indicate that not resolving these types of issues is dangerous, right down to ones own health. I blame myself for much of this. I engaged in three behaviors (among others) which proved dangerous to me. These behaviors opened doors, and they are by no means an exhaustive list of door openers. Your daughter's doors could be different from the ones I opened, but no less devastating if not dealt with. Here are my doors:
- Impurity. I'm still a virgin, but my mind certainly isn't clean. The internet is a horrible thing if abused. I'll leave it at that. I do want to point out something though. From all of the reading I have been doing recently, many occult rituals are centered around counterfeit sexuality and a perversion of what God naturally intended. That area opens up doors that should be bolted shut and guarded 24x7. If your daughter has been in any kind of contact with a peeper, she needs to seriously consider this warning.
- Pride. I was proud of my shortcomings, and frankly didn't want to change anything as I thought I was still good enough that it wouldn't matter. Deep down I knew Jesus wanted more from me, and that I was playing with fire.
-Fantasy. Not the same as the first. I got into Dungeons and Dragons, and while I'm not saying that ALL D&D is bad, the way I played certainly was. I wished I was as powerful as my character. I really felt as though people didn't take me seriously, and it upset me to no end. Escaping into an alternate reality was NOT healthy for me, especially since I don't have the ability to throw fireballs. I do have a pretty sweet set of armor though, and even a sword! Then again every Christian does.
-As a kid, I was interested in ghosts and aliens, although that had subsided by high school, it was still a huge door
Oh and door number 5 was music. I loved heavy music, and if it did nothing else, it encouraged me to curse an awful lot. I'm not saying that all Christians have to abstain from heavy music with profanity in it, but I certainly do (not to worry, there are alternatives that can not only rock just as hard, but they make you feel good while listening to them

).
Here's the thing about open doors:
-They always lead to deviant behavior (in God's eyes, not nesc. society's eyes).
-They lead to further deviant behavior if not dealt with
Back to the story; sometime during all of this, I started to feel uneasy. At night, it was like
Someone was watching me. Oh heavens it was terrifying. I remember one night waking up (or dreaming, I'm not sure) that some strange figure was standing over me wearing a gas mask with a (I think) pale face... I don't remember it having any feet either... *vomit*
Then a few days later, the big one. Some weird looking spirit that I don't want to describe for fear it might give it power
touched me. I will say this, it wasn't anything I could have possibly dreamed up. It's coloring wasn't anything organic, and it wasn't bound by the laws of physics. We'll leave it at that. At any rate, It touched me on my lower abdomen on either the right or the left side. I think it was the right, but I might have it confused as I was lying on my stomach when this happened. Several days later
I almost died.. My appendix ruptured, but I had just thought it was a really bad case of the flu (although the entire few days I had the strangest feeling that I was dying). I really did think it was the flu as I had just been to a doctor who didn't catch it (it turns out he was just really slow to process my blood work). It's important to point out
where I was touched as if you look at an anatomical diagram, the appendix is on the lower left

.
I remember lying in the bath tub trying to find relief from the pain and then screaming for my mom to call an ambulance (if I hadn't gone to the hospital, I
would have died). Apparently they said my vitals were pretty bad in the ambulance, and when I finally got scanned at the hospital, my appendix had already ruptured (rather than just being about to rupture). I do remember feeling at peace with whatever would happen because I had already been in the process of trying to get right with Jesus. It was a powerful and moving experience, and the Lord really worked in my life in the weeks afterwards. It was almost beautiful. But it wasn't a good way to find out just how strong Jesus was. I could have found that out without all the other problems. And while my appendix problem went away after surgery, my other health problems have lingered to this day (although I believe that if I turn to Christ with all my heart they will go away, that much he has shown me in the past, and I'm stronger now than I was in high school).
Oh, and I was still attacked after that. I have woken up at night with a voice that was hoarse from praying in my sleep and saying over and over again that I rebuke whatever/whoever is attacking me in the name of Jesus, and that it should go where Jesus says it should (which is NOT HERE). That never fails, either. I've not been touched since. I'm afraid of the dark sometimes though... It makes me feel like something is where it shouldn't be...
The point is pretty much:
-Don't open doors (and for heavens sake if you have any of them open, get rid of them)
-Those doors have to be opened by choice. My experience has shown that with my foolishly falling back into them on occasion like a foolish child stuck wandering the desert for another 40 years (and I don't mean for that comment to be anti-Semitic)
-Jesus is far more powerful than satan and his demons. They cannot stand in the presence of God, nor can they stand the Holy Spirit.
-Take the sword of the spirit, ram it into the enemy's chest, twist the blade, and then praise Jesus for the fact that you're free! But heed Luke 10:19:
19Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you.
20Notwithstanding in this rejoice not, that the spirits are subject unto you; but rather rejoice, because your names are written in heaven.
Oh, and coming back to music, if your daughter is on shaky ground Godsmack isn't the right thing to be listening to (at least in my potentially unenlightened opinion). The lead singer practices Wicca, and he even has a song about Voodoo. Maybe I'm digging too deeply into it, but if you're under attack in any way, that's not a good thing to be listening to.
It's a tough call about what to do when your friends play music that has the potential to be spiritually dangerous, and people hate bible thumping evangelists, but listening to it at home is certainly avoidable. I highly recommend abstaining for a while until things get under control. I do have some alternatives to suggest though

. I wouldn't recommend them as worship songs in church, but as music to listen to in private, they can serve as a great battering ram against the gates of hell. They're also fun

.
I'm probably a black sheep as I listen to what I term "fringe" CCM- heavy enough to scare some people, and yet still written by Christian artists. I feel like maybe my black sheepishness can be of assistance here. I own music by artists like Casting Crowns, etc, but I really like metal. I enjoy both heavily, but frankly there was a time when it wouldn't take much to get me to listen to metal, but getting me to listen to the normal CCM stuff would have been nigh on impossible. If you think your daughter might give it a try, I can put together a list of suggestions along with some accompanying lyrics and youtube links. Just three samples in order of lightest to heaviest:
Fire in my Eyes by Fireflight. Let's be clear, this is rock, not metal, but it's pretty awesome and I doubt a lot of people outside the church realize that this is Fireflights third (and also best) disc. There are other tracks on the disc with more overtly Christian lyrics, but this one is just insane.
http://www.youtube.com/watch?v=TJw34rxZHuEGimme Half by The Devil Wears Prada. I really like the direction their latest release went. It has a message to it if you look for it. The comments to this are pretty amusing too (although a few are crude).
http://www.youtube.com/watch?v=BR9szLl3gr8Overkill Exposure by Living Sacrifice. Not the most overly Christian track on the disc, but it can
peel paint. 
Bruce Fitzhugh's screams of "guard my heart, guard my will" are also pretty freaking awesome. The guys from LS are so talented, I've even heard of some athiests who listen and just ignore the God part.
http://www.youtube.com/watch?v=IEHkc5Ez3VsHopefully this post has been helpful. If you've got any questions or anything please don't hesitate to send me a an email or a PM. Nobody should be afraid of these spirits. They are so weak when compared to The Lord Most High. They don't go away when they aren't dealt with though, and your daughter needs to get out... NOW
Edit: Bonus Fireflight. Anyone reading this should just go get "For Those Who Wait" right now. You won't be disappointed.
http://www.youtube.com/watch?v=msDN4hA1sDkhttp://www.youtube.com/watch?v=wPOaaEV8z3Ihttp://www.youtube.com/watch?v=jnE5Ki5WdBk