WHy not simply tell SIL - sorry SD is not invited, or the invite was for you and your DH only SIL not for additional people?

I would simply tell SIL - sorry SD is not invited thus not on the guest list. End of discussion, I would not care what SIL thought

But remember Hon, this is still DH's daughter, if she comes to the party, make it clear she can not bring a guest, the guest list is full and the catering is done, also make it clear if she does not behave she will be removed as a party crasher and then let her attend, maybe she changed, maybe not... if she's still a brat DH will just be reminded why he does not speak to her and you have another couple of months SD free...

If she misbehaves, simple ask SIL to remove her, maybe SIL will see what a brat she really is...
Make sure you are always with DH, SD can't speak to him alone And ignore her through out....

Keep doing the party - it's for DH and you and show him you can deal with this nonsense... stand strong and do not let SD ruin anything.... after the party disengage from SIL as well she's a rude cow for bringing uninvited guests

I'm with Acra - why are you not texting SIL or calling or whatever and telling her No, SD is not invited?

Is there a restraining order still in place with MIL? Does your husband actually want her there? Has SIL done stupid crap like this before?

It is your and DH's party. It is your house, your event. I would tell SIL not to bring SD and if she can't go without bringing her she's uninvited? It's not her place to fix this, which may be what she's going for. It's also not her place to decide your guest list is incomplete because of her own feelings. I'd probably start with a response to her text of either, No, that won't work for us or Why are you trying to bring an uninvited guest?

So DHs sister called him when he was very busy and said she's bringing his daughter to the party.
He didn't want to argue or didn't have the time to argue so he said fine.

Now instead of calling his sister back and saying no, you can't bring her, he'd rather cancel the party?

What's your relationship with SIL?
Can you call her and find out why she wants to bring SD?
Is it possible that SIL and SD have had a heart to heart and SD is willing to behave and use this party as an opportunity to make it up to her Dad and you?

My gut feeling is to tell SIL that SD isn't invited. That there is no room at the restaurant and be prepared for drama.

DH can go out with SIL and SD on his own for his birthday.

Your dh, bless his heart, is making you the bad guy. He says yes, see what a nice guy he is? It's that dreadful wife of his who has to call everybody back, say no, and make everyone miserable. Nicely played, dh.

I'm sure he IS a good guy but these guys fall into this pattern all too easily. The tipoff is in him saying "Ok cancel the party!!" instead of "Oh, dang, it was an off moment, my bad! I'll call MY OWN DAMN SISTER and tell her what's what."

No, he's skillfully pushing it all on to you. Because he wants to be seen as the "nice guy."

My dh is a fabulous human being and I admire and adore him. But he also has this "nice guy" thing going. I've learned you sometimes have to be absolutely clear about these things or they can't hear anything but "but then I wouldn't be a nice guy!!!"

So my advice is un-invite HIM from the party. He and SIL and SD can go party somewhere and he can get stuck with the bill instead of enjoy presents and then he can sleep on the couch. Meantime, you will have a fabulous party that is now themed around your guests, instead of him. What is popular to your crowd? a college team? Halloween? Remove all references to birthday and go ahead with this other fun theme instead.

If that's too tricky for you and I understand it could be, just cancel the party. He does not get to use all the time and resources you have put into this party to make you the bad guy. No. Cruel in the extreme. He doesn't see it that way, but you have to teach him not to try it again.

It sounds like he's okay with her being there. If you're truly doing this for him then suck it up and let her come. If she is still on bad terms with so many people at the party then I doubt she'll stay too long anyway. I don't think you should cancel the party or not go. Throw the party, enjoy it and ignore the girl. It's not an end-all kind of situation. Perhaps this is the opportunity the girl can use to apologize to everyone she's offended.

I wouldn't go, if DH approved it then he can deal with it alone. I owuldn't care if I paid for it or not. It would be the last thing I paid for again. Your DH has shown you where he is on the subject, he doesn't care what you think.

1.  Back in the day I threw a huge 50th for my DH. SD (then18) shows up and immediately sulked in the corner. Wouldn't make eye contact with people. Acted like she was moments from tears. All attention getting stuff. People kept asking her if she was okay and giving her hugs, like she was a trauma victim. I wanted to stab her in the throat with a chopstick but as it turned out I managed to avoid her all night and ultimately DH had the birthday he wanted.  I think you can pull it off if you want to.

2. Just weeks ago a dear friend of mine had her 50th at a local bar/restaurant. Her 24 year old SD showed up, got sloppy drunk, showed her butt crack to the crowd as she sexxy rode a mechanical bull, puked in the parking lot and then sobbed in the corner for an hour because no one (meaning Dadee and SM) would buy her a car. And she can't work without a car, don'cha know? Oscar winning performance, really.

SDs frequently manage to make Big Events about themselves. I wouldn't blame you for wanting to cancel but it honestly sounds like he wants SD there. That's why he threw you under the bus (sorry, not buying the too nice/too busy storyline). And rather than listen to you complain he'd rather you cancel the party. I would probably roll with it at this point and throw the party. Smile and look great. Be gracious and appear completely unpreturbed.Ignore SD and SIL. Aaand then take it as a lesson learned. SIL would be seriously dead to me. I would completely detach from DH, SIL and SD shennanigans. Again, lesson learned.

Good luck. I know you are just trying to do something nice for DH.

Only those on the list to be allowed in. Let the SD sulk in the parking lot.  SIL can bring her but only SIL will enter... along with anyone else on the list.

No +1 crap. Security should only allow named individuals to enter.

That does two things. Allows you, DH and  your select friends and family to enjoy the event, and it sends a perfectly clear message to those who manipulate.

Good luck and happy 50th to your DH.  Welcome to the half century+ club.

At this point, it probably doesn't matter if you have the party or don't, you will still feel marginalized. I completely understand. I would too.

I'd consider whether you can talk to SIL and reason with her that your MIL won't feel comfortable with someone so divisive at the party. As a last ditch effort, you can tell SIL you don't feel comfortable with SD there after everything that's happened. If that doesn't work, perhaps SIL shouldn't attend either, but this won't go over well, of course.

When all that doesn't work, you can consider canceling the party or just canceling the party to family and just having friends. After that plan is in place, you can quietly let MIL know when the party is and make it clear the invitation is only for her and please keep the plan quiet. You'll know the likelihood of MIL being able to do this. If she can't keep it quiet, just have friends.

I know how you feel - you were trying to do something nice and now it's been complicated by the same little snot that has complicated everything for years. It's not fair. Your husband's response sounds like someone who is tired of dealing with both of you and that's not fair either. But if he knew how to deal with his kid, you'd probably be happy to have SD at the party.