It can be caused by lack of exercise, overweight, the rabbit being stuck on a hard or uncomfortable surface (like wire-floor or hard wooden floor with no bedding anywhere) and the cage being wet/dirty.
If she's got sore hooks she would need to see a vet.
It can get infected and thus its important that she gets antibiotics against eventual infections.
I would also make sure to clean the cage often while she recovers, and make sure it doesn't get wet. Giving her something soft to sit on is also good.
When my rex got it I moved him inside (since it was raining quite a lot) I gave him a pillow to sit on, and a litter-box filled with shredded newspaper (I didn't want to use shavings in case he got them in his feet, and I didn't know of any good woodpellet-brand at the time) he sat still on that pillow for at least two weeks :roll: only moving to eat and go to the toilet (which was lucky since then at least he didn't pee on the pillow)