Thank you for all of your input.
The reason I feel that my desire to not have her in my house may be unreasonable is that one of the things that they are working on is the discrepancy in the effort that each of them puts in to see the other. She lives an hour and a half away and my husband does the vast majority of the driving to see her. So, as part of their new agreement, she has to come up here more often to make it more equitable. As much as I don't want her around, I worry that putting that restriction hampers their efforts to fix their relationship, if I'm not going to veto it.
Marcus, we do have veto power but I would prefer not to do it. I'm generally of the opinion that he is an adult and can do what he wants but at the same time, he has a tendency to let people walk over him and I am protective.
I am hearing about all of this from my husband, so perhaps telling him that I don't want to hear about their fights anymore is the solution. I worry about not being supportive if I do that, but I know I am not going to be able to hold my tongue if I have to keep hearing about it.
As for the apology - this is admittedly one of my personal issues. I have a thing about there being consequences for bad behavior and it burns me that she gets to be a raging bitch to everyone around her and not get called out on it and gets to just go on as if nothing happened over and over again. It's one of the reasons why I asked if I'm out of line, because I definitely have a thing about requiring an apology when I feel that I have been wronged. I haven't spoken to my brother in 7 years because he was a complete ass to me and my mom and never apologized. So, I can recognize that I'm extreme when it comes to that.
I guess I'll just have to avoid her as much as possible, although I won't be able to completely since we run in the same close knit social group. I tend to be a confrontational person though and am very bad at keeping my mouth shut, so any advice on how to not rip her head off the next time I see her?