Are you able to get her scheduled for her spay ASAP? That will terminate a pregnancy (if there is one) and she will no longer be at risk of getting pregnant. Vets do prefer to wait a bit to spay females, but in this case, I would ask if it can be done now as a precaution.

I was in the same situation. My male matured at only three months and began mounting his sister. Caught him quick, but had to separate them until they were big enough to be altered, which wasn’t until they were four months. Separating them for that time didn’t really affect their bond — she didn’t like his attempts to mount and tried mounting him in return (both wanted to be the dominant bun). I was able to bond them again quickly because their hormones began to fade after the surgery, and they were right as rain together in three weeks. This might have been because I had them both done together; they both ‘smelled’ of the vet. Have you considered having both of them altered at the same time (if they’re both big enough for the surgery)?

I did exactly the same as gingerg and had them done the same day. Try to keep their cages next to each other so they can see and smell each other but not touch.

You will need to allow your girl at least 10 days to recover and your boy 7 days. The surgery should not be any more traumatic if she is already pregnant, it is generally more upsetting for the vet techs. You will probably feel guilty but the reality is many kits do not survive in the first litter and neither do the Mummies. A couple of my rescue buns were done at 4 months and they went well, even one of them that had some sort of malformation with her ovaries and a bleeding problem. That was not due to age but an existing condition being part of a first (and only) litter to a sick malnourished Mummy in the local dog pound. I got them at a few hours old, the rangers dropped them to me. I lost 3 who had health problems that just could not be over come with care, Suki had the problems and came through with flying colours and has since been adopted into a very loving home. They’ll be OK. If your vet is rabbit savvy they will know what to look for and do. Post operative care and pain management is usually the biggest thing. Start researching that and make sure you have some critical care and other goodies ready.

Unfortunately, I don’t think it’s a good idea to put them back in the same cage together right after the surgery. My vet advised me to continue to separate them during their recovery. This is in part because they will both need to have their activity limited while their bodies recover (they will need to be kept in their respective cages 24/7 so they don’t run around or jump), and part to keep them from attempting to mount each other while they recover (as that could tear their stitches, and in my case, continue bad feelings between my bunnies). After they were both healed up, I started doing supervised visits together, to watch and make sure that they didn’t hurt each other fighting; this continued to be an issue for the first little while because my boy still had his hormonal urges to mount. This dissipated very quickly, in my case, and they were able to go back to living together quite soon.

Oh, and your boy will show some hormonal behavior weeks after so I would allow a few weeks then slow introductions.