The trim trax can cut their nails too short, I only ever have them in the wheel a day at a time, as needed. If their nails get too short, they cannot cling to things or grip properly. Hopefully that's the issue and you can take the trim trax out and see. But if it's only one back leg she might be hurt. Look up the symptoms of hind leg paralysis as well and make sure it doesn't seem like that. Try holding her and gently pull back on each of her legs and see if she reacts differently or if it seems to hurt. The vet did that once to check for muscle weakness/pain, so maybe if you can test her reaction for one hind leg vs the other it'll help you know if something is wrong. If something seems wrong or she stop using it or something she absolutely will need to see the vet. Side note, ours fall and fling out of the wheel all the time and act like it's fun. So falling doesn't necessarily mean she's hurt, but of course falling isn't a great thing to do... good luck!