Definitely her behaviour has been inappropriate. However, I completely understand you wanting him to be able to have her at your wedding as she is a close friend of his. My suggestions is tell your FI you appreciate that he is seeing your side of this and that he was willing to not invite her however you realize she is important to him and therefore you think she should be invited. THEN I would have a conversation with the girl. I think you need to sit down with her face to face and talk. Not be catty, but just let her know that you think some of her behaviour is inappropriate. That you realize she is important to your FI so you don't want to get in the way of their friendship but remind her that there are boundaries.