Hate my brother-in-law's gf and don't want her there.

You're in the wrong here. 100% the gf should be invited. I don't blame your FBIL for saying he wouldn't attend if his gf wasn't invited. I would hope that your FH would support you the same way if you were ever purposely left out of a special event.

I know how you feel. I have someone coming to my wedding I do not want there. You're not wrong to feel how you feel. You have feelings and you're protecting your heart. Unfortunately though to keep peace you're going to have to invite both of them or neither of them.

Agree....they're in a relationship and unless she's abused you in some way, disliking her isn't a reason not to honor FBIL's relationship. You certainly don't need to put her in your wedding party! But FBIL is right to "threaten" not to come if his significant other isn't invited.

Agree with PP's. I think the term "nearest and dearest" is used a lot on these forums when referencing your bridal party. She should be invited, by name, as she is your FBIL's significant other.

I think the first response you have on here is completely true. I imagine you would want your FH to stand up for you, had it been the other way around. Be the better person. It's likely you won't even be around her much once the day comes.

I may be the minority here, but it is because I know how it feels to not want toxic people around. My first instinct is to say forget her, its your day to be selfish and include ONLY the "nearest and dearest." However, this situation is messy - the FBIL should not have given an ultimatum, but that is his significant other. She may be his long-time girlfriend now, maybe his wife down the line. How would you feel if your FH is invited and in the wedding, but not you?

Ultimately, you will have to choose both or neither. I believe choosing neither will negatively affect yours and FH relationship with FBIL, or worse end it indefinitely. If you and FH are fine with the possibility losing that relationship, then move forward with the day without either of them.

Out of curiosity, and because she sounds like the type, do you think if she was only invited to the wedding but not in the wedding party she would do something disruptive or disrespectful at the wedding or reception? Maybe extend an invitation to the wedding, but have a conversation with Baby Brother explaining your concerns and why you initially didn't want her there. He might be able to make sure she behaves that day.

You have every right to not have her in your party, but you do need to invite her to the wedding.