I had the same problem with my 16 year old daughter. Had, being the operative word. It dawned on me one day that the most effective way to deal with this situation at this point, (after several years of battles, attempts at reasoning, awarding an allowance for cleanliness), was to go into her room one day while she was at school, find something she loved and destroy it, not saying a word about it.
I saw her treasured and very expensive lap top (a present from her grandmother) on the floor under a pile of dirty clothes, instead of being in the computer case where it belonged. I accidently stepped on it, and cracked the screen. OOOPPPSSSS! I said nothing to her.
About 2 weeks later (yes, it took her 2 weeks to dig her lap top out from the pile of dirty clothes), my daughter comes to me, very upset, and says "Mom, I don't know what happened, but my lap top is broken." Exhibiting extreme motherly concern, I asked her how she thought that may have happened. She said she had no idea, then I asked where it was. She said on the floor of her bedroom under a pile of clothes. So then we both surmised that she or one of her friends must have stepped on it without realizing it. I then told her that had it been in the computer case, whatever happened to it probably would not have happened. She couldn't argue.
Now my daughter is faced with two problems, 1. she'll have to save enough money to purchase a new lap top (before she goes off to college next fall), and 2. find a way to tell her grandmother that her lap top is broken.
Oh, by the way, her room has never been cleaner since that awful day of disclosure. It's now been 3+ months...
Unfortunately sometimes kids have to learn things the hard way. You know what your child responds to better than anyone else, but sometimes tough lessons can be very effective. As we all know, girls can be very stubborn, so being a step ahead of her will serve both of you well.