Hi there, welcome 🙂
So, it used to be more common for unspayed females to be bonded with neutered males (back when it was impossible to find a vet to spay females), but it is more challenging and more likely to break at some point. It depends a lot on the buns personalities and whether the male mounts obsessively. If he mounts her a lot it will be very stressful for her as it will trigger false pregnancies. So as you proceed just be very aware of how much he is mounting her and her stress levels (esp given her health was poor enough to prevent spaying her). How old is your female?
You will want to start very slowly. A long pre-bonding period should help him get used to her scent so she isn’t so “exciting” to him. If you don’t have them set up this way already, you should set them up in side-by-side pens and then swap who is in which pen every day or two for several weeks. If that’s impossible you can swap litter trays (when they are at least sort of dirty).
Then all the usual bonding steps apply, you will just want to be extra sure you are good at each step before moving forward. Have you bonded bunnies before?
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The answers provided in this discussion are for general guideline purposes only. The information is not intended to diagnose or treat your pet. Seek the advice of your veterinarian or a qualified behaviorist.