I just got the feeling she might be jealous because of the way she seems to be making sure that you are fully aware that he is doing oh so we'll since you both split up. Almost like a passive aggressive way of making sure you don't try and get back with him. I get the feeling she is quite loud? When you started seeing her brother do you think she may have felt like you took some of the limelight off her? I wonder if she doesn't like the idea of her brother getting close to another woman because its HER brother and she wants the number one woman spot in his life. All sounds so Freudian doesn't it?! Either way she sounds like a right cow!