Sorry you are not invited to my wedding?

That is a good idea! Thanks!

Maybe you have a friend or relative who you can put in charge of "drama control" or something...? Someone to make sure that your sister and your dad do not get too close to each other if at all possible...? We don't want to invite my FH's sister because she's drunk and inappropriate at every function that she goes to, but we figure she's family and we can't exclude her. However, my sister and my FH's Mom are planning to keep a very close eye on her to ensure that she gets cut off from alcohol before she starts acting up. I don't know if something like that would work in your situation since you said your Dad would leave as soon as he saw your sister. Maybe you can talk to him and explain how much it means to you to have both of them there. You can even tell him that he doesn't have to talk to her or be near her at all, the only thing you ask for him to just not fight with her. I think that's what I would do - I would just tell them both that they better be decent human beings for one day for my sake. Everyone should be capable of that.

If you don't want her there then I would just respectfully tell her the reasons why.

Are you and your sister close? Does she have to miss out just because your dad doesn't want to see her? In the future, do you think you'll look back and regret her not being there?

If so, I'd hope they can both be grown up enough to at least respectfully avoid each other for the night. It's who you want to be surrounded by and celebrate with that should be there, and ultimately this decision is made by you, not by somebody else who says they'll leave if they don't agree with your guest list.

Without knowing the background I would suggest your talk to her (and possibly your father as well) but you can tell her that for your wedding she needs to work things out with your father, a temporary cease fire or a reconciliation that is up to her. If she can't or won't then she isn't welcome at your wedding, you can tell her that it isn't fair to make you chose between the 2 of them but if that is what she wants then you have chosen and her war with your dad DOES mean that she misses out on important events. Put the choice in her court, your father will be there and you don't want the war at your wedding she can choose to either fix the problem or not attend she can't have a battle at your wedding. I would also talk to some of your friends and family and task them with making her leave if she does show up. And this might start a war but that is your sister's choice.