What kind of mites are your rabbits getting? If it's Demodex mites (which tend to be more common) they naturally live on the rabbit and only overpopulate to cause problems when the rabbit's immune system is compromised or suppressed. Demodex is common in very young animals that haven't yet built up a strong immune system for this reason. In dogs, Demodex is typically treated with medicated baths, but I am not sure how comfortable most vets would be using this technique on a bunny. Sarcoptic mites do not live naturally on the rabbit and would recur because the medication is not strong enough to break the life cycle or because the rabbit is being continually reinfected by their bedding, toy, or pretty much anything they came into contact with while having the mites. Sarcoptic mites are pretty rare in pet rabbits, however, and I have no idea how she could have gotten them unless she picked them up off your clothes from a wild rabbit or infected pet, or if she's new to your home and picked them up in a previous location. Good luck!