Why is my female rabbit's vulva swollen after humping her sister?

Thanks for reaching out. Not all individuals get along, especially in confined areas. As young rabbits mature and hormone levels rise, territoriality and dominance are fought over to establish. Spaying the rabbits is necessary anyways, so now might be a good time. Keep separated for now. Good luck.

Thanks for reaching out about Bun Bun. This question has been addressed once before but there recommendation is to have Bun Bun spayed, and Fluffy neutered also (if not). Intact female spays have an increased incidence of uterine cancer but also tend to fight more. Talk to a veterinarian in your locale. Good luck.

Thanks for reaching out about your rabbits. Not an uncommon response in intact females, protection of the warren. Both rabbits needed to be spayed due to the high chance of uterine cancer in rabbits. Good luck.

She has an infection. It may just be the external structures you can see or it may be coming from the inside (either a bladder infection or a uterine infection). If you have tried to breed her and she isn't getting pregnant then she may very well have an underlying uterine infection. I suggest you get her to a vet for an exam. Hope this helps. Best wishes.

This is part of dominance behavior, and the one humping the other is showing she is the top bunny. I wouldn't be concerned about it, but I would stop any aggression and separate them immediately. By the way, I love their names :-)

Thanks for reaching out about Fluffy. This is probably a response to reproduction, the release of pheromones in the urine and dominance. Rabbits have a high incidence of uterine neoplasia and should be spayed. This will probably cure this behavior also. Good luck.

Thanks for reaching out about Zoomie. Most likely it is because she is an intact female, and is fighting for territory and dominance. She needs to be spayed to prevent uterine neoplasia anyways, so now would be a good time. If she continues to be aggressive to the dog and cat, something bad is bound to happen, so isolate her for now. Good luck.