Sorry to hear she is biting. It's par for the course with rabbits. my rabbits are really nice and will generally tolerate a lot (grooming then, giving medicine, etc) before they bite. But nursing mothers you can count on to be cranky. Their hormones are all mixed up and they are probably fearful something will hurt their babies. At this point, I would chalk it up to the fact that she just doesn't know you very well. If she was not socialized and handled a lot in her previous home, that is a part of it, too. Bunnies dislike change and she has gone through a lot now.
However, there is always the chance that she could be pregnant, so if in a few weeks she starts to get more aggressive, especially towards the kits, you should remove them and just let them nurse twice a day. If she does have a second litter, then you will have to let the older ones wean. I say this because occasionally pregnant mothers, especially when they are very near giving birth, hurt other rabbits, even their own babies.
Right now I think she just doesn't know what to make of what is happening. She hasn't had enough time to really trust you yet. Be cautious when putting your hand in the cage. some of my bunnies are very territorial about their cage and get very annoyed when I put my hand in to clean, even though they are fine with me handling them outside the cage.