If emergency spay would be unavailable or too risky And she is indeed pregnant, there's not much care needed from human as she will take care of her kits herself, there's a very little assistance needed you can start thread here and post all your questions and pics and we're happy to help if you don't know what to do.
For now (if she's really pregnant), you have one month before babies arrive you don't have to do anything, I would say if you can separate them completely that would be much better. On day 28 you will have to give her a nest box (it's not difficult to make diy) or maybe a bit earlier if you see she is pulling her fur or carrying hay in her mouth and building something in the corner, but can also be a false pregnancy because she's so close to unneutered buck.
When babies arrive you will have to check if they're all alive and moving and just leave her she will feed them and will take care of them. At about 2 weeks old they will grow and will start jumping out of their nestbox so it'd be nice if you can give her some extra room because she can get stressed they will follow her everywhere begging for milk so just give her an extra shelf where kits can't reach her or something. She will feed them until they are 6-8 weeks but they will also start eating hay and some pellets from her bowl when they are 3-4 weeks old.
At 8 weeks old you will have to find new homes for them you can just place an ad on your local board and see if you can find nice people looking for a bunny, some people would take two so they could keep company.
She can have 1 to 10 babies there's no guarantee how many she'll have maybe 4 maybe 6, if more maybe not all will survive.
But honestly as you say she's 13 weeks old she's a bit too young to get pregnant, she's almost on edge so this mating is like a rehearsal maybe and you're maybe lucky and nothing will change for you this time. But she can be fertile already, usually they say from 14 weeks depending on her breed.
Anyway, don't panic separate them completely until your buck is neutered and healed and wait about 4 weeks if she'll start building a nest (she can also start at day 17 then it will be a false pregnancy and will last a couple days then she'll be back to normal). Keep in touch we're happy to help