Please read the Unabridged Guide to Litterbox problems on the Cats International site. It has the best information I've ever read about why cats have problems and what to do.

http://www.catsinternational.org/art...ing/index.html

I feel confident that with your love and care, she'll come around and cope with whatever has disturbed her. As Jenn says, sometimes it take retraining. But it's doable!

Good luck to you and her.