If it's mites, antibiotics do not help. Mites are a small parasite, and they need some sort of anti-parasitic (like Revolution or Advantage but NOT Frontline, which is poisonous to rabbits.)
It could also be some sort of fungus picked up from the soil.
If it were my rabbit, I would work with my vet, and treat with my rabbit with Revolution (which will kill any and all external parasites common to rabbits), and then start her on an antifungal orally to see if it affects these weird growths.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry