The only family member my husband has is with the most dirty woman. She can't care for her son, can't keep her home clean, doesn't work, cheats on my husband's cousin....and flirts with my husband every chance she gets. In the beginning, I tried to be gracious and position myself between her and my spouse. The cousin is the only family he has...right. Later, I told the husband that the cousin is welcome but I just don't feel up to entertaining his girlfriend. Just too much to do in the house. She used that as an excuse to hang out with the guys and drink beer. Found her dancing with my drunk husband. Smacked the s*&t out of him and grabbed her by the back of her hair and we had a private conversation in the barn.
This was before we got married by the way. My husband seriously can't see her flirting but I and any other woman here can see it just fine. He says she is my cousin's wife and sees her like his cousin's watch or coat. I now realize over the past few years that he was serious and really doesn't see her as the threat I do. Needless to say our "conversation" put a stop to her coming. She is now sick, having to visit her sister, etc. Maybe just take the woman to the side and explain how much you love hearing about the ex and go into great detail how much you would like to see her elsewhere, in pieces, etc. The conversation doesn't have to be physical or particularly ugly but it does need to be honest. Don't sugar coat and try to soften things with her.