The pregnancy theory has merit. Since she was housed with another rabbit she may have a false pregnancy. She will think and act like she is pregnant even though she isn't.
False pregnancies usually end within 3 weeks, though I have had does go a full 31 days. If that is what is going on, she will probably pull at least a little fur at some point.
Unfamiliar situations can also cause a normally good-natured rabbit to act aggressive. I once had a Harlequin doe that was named Dora the Explorer because of her calm, inquisitive personality. When I took her to her first show, though, it was a bit too much for her. When I put her on the show table, the judge was a bit peremptory in his handling, and she got scared. She started growling and even smacked at him a couple of times. Normally, you try to keep out of the judges' way as much as possible, but I could see that he was very close to disqualifying her for being vicious. So I stepped up to the table, and poked her backside to get her to turn and face me. When she did, I said, "Hey, Dora! Easy, it's me," and started petting her. She put her paws on my shoulder and snuggled her head under my chin. I cuddled and petted her for a minute or two, until she calmed down enough to put all four paws back on the table. I told the judge, "sorry about that. She's not mean, just a bit . . . overwhelmed." She was fine after that.
Run-of-the-mill possessiveness is another matter, and whether I put up with it depends on how bad it is. I try to keep my hands high when going into the cage - high posture equals high status to a rabbit, low is submission. If I need to handle her, I wait until she hunkers down before picking her up. Going in low and in front of a rabbit that is standing tall is a good way to get scratched or even bitten!
