Depends on how your little girl develops, if she is mature enough and you have a good vet they can be done from 4 months, some vets like to wait until they are 6 months old, but it should be when they weigh enough and are mature enough which of course varies from bunny to bunny.
When she gets to 12-14 weeks normally you'll see her start to become hormonal, she may be more vocal, or start to jump on you boy and become territorial. Saffy was a rescue baby bun and was a nightmare, i had to have bars between them for 2 weeks after she started to become hormonal and joey got fed up of her jumping on him, he pushed her off and she had a go at him which ended up with a nasty bite to her ear and a big vets bills
they did rebond fine after her op. Yours may well be fine but just keep an eye on them, especially her and her behaviour.