First off !! I would wait until after she has shed, then put the rat in with her. Keep an eye on her though. You don't want the rat to try to bite her if she isn't going to eat it right away. If she doesn't eat it, then you could either keep it or take it back to where you go it. If from a pet store, then they will likely take it back, but may not give your money back. Hope this helps.