If you think she is under the vanity you can pulll the face board/kick plate off. It will probably break up if it was glued on so you would have to replace it but that is not a big deal. At least then you will either have her back or know for sure she is in the wall. I agree with danojeno about fessing up. If you're old enough to move out on your own, then you're old enough to face the consequences of your actions and its only fair to them. Best of luck.