If she got in to his cage it is extremely likely she is pregnant. She will be due to have her kits about 31 days after she was with the buck. You should get her a nest box. You can buy a rabbit nest box at Tractor Supply, or there are a lot of DIY ideas on the Internet. You will need to give her the box around 28 days after she was bred. I usally put a layer of pine shavings in the bottom and plenty of hay on the floor and in the box for her to arange as she pleases. Very soon before she kindles she will pull some fur from her belly and put it in the nest. A lot of times I don't see my does pull fur, I just see a pile of moving fur in the nest after they are born. After she kindles you need to check on the babies to make sure there are no dead ones. If she is acting protective of the nest you may have to keep her occupied with a treat and/or remove the nest while you check the babies. After that you will just continue to check on them once a day to make sure they are fed and all are alive. At about 3 weeks old the will be getting out of the nest to eat solid food, and they can go to new homes around 7 or 8 weeks.