I've adopted all my past rabbits from rescues, it's just that my boyfriends sister is looking for homes for these babies (she bought two males as pets but it turned out one was female - they are not together anymore so no more babies!) and she now wants to find good homes for these babies. It definitely wasn't an intentional breeding, and part of me would quite like a baby rabbit once as I've never had one. I think I want rabbits for a long time, I'd like to eventually get a conti but I don't think nows the right time. I'll think over the next couple of days, Izzy seems ok but I guess I don't really know how she is
I thought I'd add my two cents, as Monty was fairly young when we got him - approx. 11 weeks, so possibly slightly older than the baby you're thinking of, but about the same age. It's been brilliant watching (and feeling!) him grow bigger and gain more confidence, and each "step" has been like a milestone. I also think there's been some benefits we may not otherwise have had - he's always been very relaxed about house noises (except the doorbell/front door) and has never sprayed or become agressive over territory, he seems to have slipped in quite easily to living around us and our weird human foibles. That said, he was very hard work at first. I know I've mentioned before that he would spend hours sat in a corner of the sofa, weeing and pooing quite happily over it; he also didn't understand how water bottles worked, so for the first few weeks it was impossible to monitor water intake, and it also took a few days to get him used to a smaller food bowl; we haven't yet had to do any official litter training, we've just provided boxes with newspaper/hay in them and he has used them, but I get the impression we've been quite lucky there; it also took him about three months to work up the courage to leave his main room and explore the rest of the flat, and he still hasn't ever been in the kitchen. I completely don't regret getting Monty and I would do it again in an instance, but I don't think on the whole he was the best bunny for a first-time rabbit owner. That's partly his background (he was an outdoor bunny on a farm, and then became an indoor bunny around humans all the time) but also that he seems to have lacked some of the knowledge that an older rescue bunny might bring with them. That said, he doesn't have any of the (I can't think of a sensitive word, sorry) "problems" that a bunny who hasn't been in the happiest of homes before going to rescue might bring. For almost all of his life he's been loved and spoilt and kept safe, and I think that shows too (having had a rescue bunny who hated humans when I was wee)
tl;dr they're very hard work - I think, reading stories, probably more so than new adult bunnies would be. It can be rewarding, but it also takes some time and some patience - and more skill than I think we had (I'm not sure who was more stressed by things like nail clipping, but I know we could have done better!) I don't know if anything in that ramble helps
Good luck making a decision, and don't feel guilty either way - I'm sure your boyfriend's sister will understand if you think on balance a baby rabbit wouldn't be the best fit for Izzy. Perhaps you could try and organise a small "meet" to see what Izzy thinks of the proposed companion?