My usually sweet 3 month old rat inflicted some serious bites on me last night

I have 2 female siamese rats. The smallest one appears to be the alpha rat which is fine because her sister dosen't seem to mind too much. However last night while out for play time my little alpha rat for no apparent reason nipped my finger and then when I tried to move my hand away she locked onto my finger inflicting a very painful and nasty puncture wound and a bruise from the force of hanging on. She then ran up my chest to my face and bit me hard on the lip. My husband waited a few minutes while i was bleeding profusely from my lip then picked her up to return her to her cage. She then bit him hard on the thumb. This is the first time this has happened she is usually a sweet, affectionate and spunky little thing but never has she even attempted to hurt either one of us. I'm really upset and concerned and would really love to hear from someone who knows about rats. How do we handle her and this behavior and what can we do that this dosen't happen again.

I had a female rat once who did the very same thing. She was always very sweet, and then one day, out of the blue, she would run up to me and bite me in my finger, and she drew blood. It happened very fast. And it happened at least once more that she would draw blood from me. Every since that first incident started, she would always go after my hands and fingers, very determined, and I knew she was out to bite me. Needless to say I became very scared of her and could hardly handle her. I would always hide my hands in my sleeves when picking her up, or wearing thick gloves. I tried to handle her as little as possible.. but I wasn't happy. And I had no idea why she became so vicious all of a sudden. She had 2 female cage mates and was never agressive to them.