This new behaviour could be caused by a few things. First possibility is that she's beginning to get her hormones or the second and more likely possibility is that she is pregnant already.
I would suggest taking a look at this thread:
http://rabbitsonline.net/view_topic.php?id=20972&forum_id=8
A similar situation to yours. Bought to rabbits of the same age, and one ended up being a girl. She go pregnant very young, and ended up almost dying because she had a stuck baby, and she was very lucky that the timing worked so well for her because she could have very easily bled out over night.
With the small breeds like you have, the risk of complications increases. Since she is so young, the risk increases as her body is not fully developed.
I would keep your male and female separate at the moment. And then take them to a rabbit savvy vet as soon as a they are open. Have your girl palpitated to see if she's pregnant (my guess is yes).
My personal advice is to spay your girl if she is pregnant. The risk of her dieing from birth at this young age is very high. And spay her now anyways if she's not pregnant, and it will help with her hormonal aggression.
The male should be able to be neutered now. Pick him up and check for testicles. They do have the ability to suck them back up sometimes, so he may decide not to show you. You can also have the vet check and see if he's able to neuter your boy.
I would suggest you tell your friend to find a rabbit rescue to get some babies from. There are tons of babies available at shelters and rescues.
I think you will find you will be very happy with your two little bunnies once they are both spayed and neutered. Their hormones will dissipate, and they will become much friendlier and less territorial.
Please share your experiences with us and keep us updated with what choices you are making so that we can help you with whatever route you decide to take. We are here to help and support you with what ever you decide to do. The route I suggested is the way to minimize the risk of losing your little girl, but the choice is totally up to you. I will give you advice to the best of my ability no matter what your choice.
Good luck, and if possible, post some pictures?? We all love pictures!
--Dawn