There is a long history of family drama and my family is just overall toxic, but there is way too much to explain everything here 
Long story as short as possible, my parents have hated each other for at least twenty years. Both of them have their own issues, but my mother has been especially nasty. They have been divorced for almost 10 years. My dad has been dating a lovely woman for about fours years now and my mother has been insistent that she not be allowed to come to the wedding. My dad and his girlfriend live together, she makes him very happy, and I have absolutely no problems with her, so I have put my foot down and told my mom that she is invited and she's going to have to just deal with it or she can just not come. This woman is very important to my dad and I think it's the right thing to do. My mom has gone totally ballistic. I am getting ranting, nasty emails that go on for pages. She refers to this woman as "your dad's filth" no matter how many times I have told her I will not tolerate that. Every time she does this, she is trying to put me in the middle of their relationship and I am done with that and will not accept it. I stayed firm that his girlfriend is invited, so she caved and asked me to put her in the back row. I also stayed firm that she will be allowed to sit beside my dad. She's incredibly upset about that, but there's nothing she can do to change my mind. She's being a child.
On top of this, she hates my half-brother; my fiancé; my fiancé's parents that she has never met; and obviously my dad and his girlfriend. Now that we are less than two weeks from the wedding day, she has been sending me hate-filled rants about all of them, even claiming that my future father-in-law looks like an alcoholic. He's not (and even if he was, i) it's a disease, and ii) that's none of her business). She's just saying it to try to be mean. While the emails are new, the hatred and vitriol are not. I have not shared any of the planning with her for the entire year and a half we have been engaged because any time I try to include her just a little, she says or does something that ruins it.
I have set boundaries, put my foot down, and refuse to engage in any of her insanity, but I'm very anxious that she's going to be nasty at the wedding and steal a part of my joy in the day. I'm also terrified that she's going to embarrass not just me, but my fiancé, as well. Our friends and extended family and colleagues/bosses will all be there. She has promised that she will behave (really she said that she would "endure dealing with all of the a**holes" so that she can be there...charming, right?), but at this point, there's a big part of me that just doesn't even want her there anymore because she is being so toxic. On top of that, she's insisting that she needs to be honored as mother of the bride and that it's an important day for "us." I have told her that I want to share the day with the people I care about, but ultimately the day is about my fiancé and me. I have told her that if she can't be supportive of me and fiancé, and be kind and supportive to all of the invited guests that play unique roles in our lives, then she doesn't need to come. I can't bring myself to uninvite her because I don't want to break her heart. It makes me sad to think about her sitting at home alone on the day her only daughter gets married.
