Amanda, yes - it's perfectly fine to keep her on mice. If you want to try to switch her for convenience sake, then you can try a few things. Get some mouse bedding and put a handful in her enclosure about 1/2 hour before you put the rat in. Get a white small/small rat and then put it in with her.

I've found that simple "tough love" works best. I stop offering mice completely - when they get hungry enough, they'll take the rat. It usually takes 4-5 weeks of tough love with a stubborn one to convert.

But if you are comfortable keeping her on mice, it's not detrimental to her at all.