Abby's Temper

Abby came to us through a rescue group, her former family relinquished her because she was "too affectionate". Her manner is typical of the Manx. She is a cat that wants to be a part of whatever you are doing. She has one behavior that is difficult to understand, she will bite or nip. I have been working diligently with her since June, and her nips have nearly stopped, but this morning she bite me and she meant it. Her former owner told me that she would nip, and that they controlled this by "bopping" her on the nose, well if someone was hitting me, I would nip at them too. So, I understood her nipping. But, I am at a loss to understand why she bit me this week. I had offered her my arm which is what she generally likes, because she will come up and head butt me and then I will slowly pet her on top of the head,and rub along her jaw, which is what she really likes. When I offered her my arm she bite my wrist and then grabbed me with her paw. Her claw got hung up on my clothing and then she bit me again and then finally in my struggle to move away from her she stumbled and she got me one last time. She made several small scratch marks, and to be honest I am not sure if it was from her claws or teeth. If she had really MEANT to bite I am sure she could have gone through my wrist pretty cleanly, but she didn't go that far. I am just confused by her behavior, and I don't know what I did to spark her reaction. I know that in her mind she had a good reason for doing what she did, but she has me totally perplexed, and she hurt my feelings. I don't suppose she meant to do that, and in all likelyhood doesn't even understand that principle. I am sure when I see her at home later, she will have totally forgotten the incident, and be her normal self. But, I have to wonder will this happen again?