Hiya firstly rule number one with bunnies, DONT PANIC :shock: :shock:
I assume Barney has been neutered?
If not, I would not advise putting them together until he is, and allowing six weeks post op. for the hormones to settle down, else you risk pregnancy aswell as accidential injury.
If putting bunnies together for the first time, it is very likely that mounting will take place as it is a natural way a bunny asserts his / her authority over another bunny.
Having said this, if it is just mounting but no actually biting that is taking place then everything should be fine.
IF Barney is neutered you could try bonding them but with caution as your Doe is so young. Perhaps only allow them to spend a few hours together to start with supervised, and split them up at night so they can have a break from each other.
I would be concerned however that your Doe may be stressed by attempting bonding at this stage, as she has only just arrived in a new home, so needs time to get used to her environment and you first :wink:
Where are they kept? Do they have a lot of room to run about in or are they confined in a hutch?
It is important the Doe feels she can get away from the Buck if she wants too, as like humans, bunnies need their own space from time to time.
I hope this helps?
best wishes