You are not alone with the Warriors series. Apparently, I'll have two warrior cats in my household for Halloween this year.

I've been doing a lot of internet searching for "If you liked the Warrior Series". Here are some of the suggestions:

http://www.downersgrovelibrary.org/kids/books/booklists/erin_hunter.php

http://www.librarypoint.org/bm_the_warriors

http://read.poudrelibraries.org/kids/z155.html

What does she like about the books? Is it that they are about animals? Other worlds? Female protagonists? That might help guide what other books you can suggest.