I’m sorry you lost your Oliver.

The bun mom might feel protective about her kit. She could still be feeding it, even though the baby is probably also quite a bit on its own. She’s still dealing with some mom-hormones and she’s in a new environment that probably doesn’t resemble her old home. If she is eating and otherwise seems healthy, I think maybe you just need to give her some time to settle in? Try to not handle her more than you absolutely have to, give her places to hide (upside-down cardboard box with 2 door holes). She’s most likely not unhappy with you at all, it’s just that moving to a new place is stressful, she has a baby and as you said, her body is already stressed from her  having been pregnant, she’s probably had more than one pregnancy.

As for spaying her, it is the best thing you can do for her longterm health. It doesnt have to be done asap though. You can let her recuperate and regain her strenght.

My recommendation is to have both spayed– this is not only crucial for longevity and for their individual behaviors, but also because regardless if they are related or not, a pair of rabbits where at least one is intact (i.e., not spayed/neutered) significantly increases the likelihood that they will not have a stable, long-term bond. Young rabbits will get along with most other rabbits due to lack of hormones; however, this changes when they begin developing hormones and will have the territorial/mating/dominance urges that causes rabbits to fight (again, regardless if they are related, raised together, etc…. rabbits do not acknowledge family units or “childhood friends”). It is called the baby bond phenomena. If you intend to keep both rabbits, both should be spayed to increase the chance they’ll have a stable, adult bond when both are grown.

There will likely come a time when you need to house both separately for their safety, as the baby will not be able to be spayed until 5-6mo old. 2.5yo is not an old rabbit by any means, so unless there’s something else going on, post-recovery from her most recent litter, she should be fine for a spay. Consult with your rabbit-savvy exotic vet to ensure all rabbits are healthy enough for a spay.