Getting Bonnie spayed

Good for you!  If you can afford it, I'd get them both done at the same time so you're not having to go through the process a 2nd time.  They shouldn't need to be separated as they are pretty self-limiting after surgery.  We usually confine our kitties just until the wooziness has worn off and they are stable on their feet again, then they get free run of the house.  They will be pretty sore, so don't expect much out of them for a couple of days.  Keep an eye on the incision sites, be sure they eat and potty, and things will be okay.  I think the process is harder on us than on them!

I think it would be fine to get them both done on the same day. It might be advisable to keep them separate for a little bit at least to stop them from hurting each other or themselves, it is likely the boy will recover faster since the surgery is so minor. You'll want to keep the female apart to recover for at least the first little bit after the procedure to observe her and make sure that she starts eating, drinking, using the litter normally. They can be together soon after. Ours was spayed while still at a foster family with many other kittens and they were fine being together.

I agree, if you can afford it it makes sense to get them both done at the same time.  It is bigger surgery for females usually so she will take longer to be fully active but at least they would both be a bit sore together just afterwards.  It would also avoid that stress of bringing each one home to their sibling smelling differently and going through the introductions when the 'invader' is the one likely to be mistrusted.

I had my previous 2 female litter sisters spayed at the same time.  It also gets your own worry over in one go.