So my sister is diagnosed and I would like to understand her behaviour. I am not quite sure if she is the bad person, I think of her or is it her illness?

In the past years, she has always started extreme fights with our family. She is always screaming, crying and finally "flees" from the house. The reasons were usually relatively trivial. It was mostly about finances and the inheritance. During these fights I always thought she was crazy. Is this normal when one suffers from anxiety disorders or does it already indicate something else?

She was also negatively obsessed with my brother-in-law. He is the worst man ever and an absolutely disgusting man, in her opinion. (To me he is like a brother.) But to help and especially to comfort her is he good enough. (He doesn't know what she said about him). Maybe she sees him as a threat? I don't really care, I've already formed an opinion about her. But is that also typical?

Thanks for your help :)