My future MIL has changed her mind about coming to our wedding in October 2016 pretty much since we told her of our engagement. She's gone from being excited and wanting the plan the rehearsal dinner to saying she wasn't coming at all and not to send her an invite, all in one week! Now, the wedding is far enough away that I've just been letting her go back and forth (she recently called up my Fiance and left a vm on his phone saying she wasn't coming when he didn't call her back because he was at work) but I'm not sure when I should put my foot down and take her up on the "not coming to the wedding" threat. I've never had any real problems with her, personally, and I certainly do not want to un-invite her (she is my Fiance's mother, after all) but I also do not feel like have her threaten to not come to her son's wedding simply because she isn't getting her way for the next year.
There is also the added bonus of her having issues with both of my future Brother-in-laws, and I'm a little afraid she will end up making a scene at the wedding. both of the brothers are really great, and I'm sure if I ask they'll deal with her, but because they refuse to speak with her I'm afraid she's going to turn my wedding into a therapy session for herself. Does anyone have any advice on how to speak with her about these threats and her possible actions at the wedding?