My Fiancés ex won't go away.... 6+ years?

[MommyOf2]

my fiancé and I have been together since 2008. He was dating a girl in high school on and off for 3 years. It is now 2014 and she still comments on everything his family posts on Facebook. I've tried asking her to please go away but she tells me I'm stupid and she's an adult and she can do whatever she wants. one reason I'm against her still being in his families lives is because the two break ups that me & my fiancé went thru she not only contacted him , but stalked my social networks and added my new boyfriends... Crazy much? We are expecting our 2nd child together and she is married with her own child and husband so why is she still all over his families stuff?? It is annoying, I'm not jealous at all either I just find it disrespectful and currently I am blocked from her Facebook ( I get blocked and unlocked every other month) for no reason at all... I don't speak to her! Help me.... It's causing arguments in our relationship.