I think I know that is happening. You are not able to recognize her non-verbal signals that say that she is getting angry.
People communicate to each other without words, by gestures, posture and the sounds of their voice. This is non-verbal language, and autistic people find it very difficult to understand non-verbal language, its like being a bit deaf. What I think is happening is that she is getting angrier and angrier but you don't notice, until she eventually screams, argues and jumps up and down. So it seems that she is suddenly angry for no reason.
It happened to me too. I had a female friend who had a short temper, but because of my AS I could not read her subtle signals that said that was getting angry, until she suddenly (from my perspective) shouted and screamed at me for no reason. I also thought she was mad. But she was not mad, I had a difficulty in reading her emotions.
The best thing to do is to tell her that you cant read her emotions and that she needs to tell you when she starts to feel upset. Otherwise, she will start to feel like you are deliberately ignoring her feelings, and you will think she suddenly get angry for no reason. One of the unfair things that women do when they are angry, is that they go very quite (the calm before the storm). This can mislead an Aspie into thinking everything is ok when it is not.