I vote for a champagne brunch solo or with a girlfriend instead! Let DH deal with HIS bratty.

Nope.  She can't resist.  It would be a sh!tshow.  SO either won't see it or won't react.

I know how anxious I get about seeing SD60 so I understand how you feel.  But in this case, I'd go.  This is like a "meet the fiance" event.  Bratty will probably be on her best behavior.  Who knows, Nutter GF might even be a positive influence on Bratty.  It's also a support to the family, putting the family's best foot forward with a new inlaw.

It's only a meal.  It will give you a chance to assess Nutter and also see how DH responds to any slights.  Like me, you will have to accept that as his daughter, Bratty will be in your life as long as DH lives.  That's been hard for me to swallow but "mental health is an ongoing dedication to reality at all costs". 

DH made some pretty strong statements about leaving if Bratty does something Bratty-ish. Thi would put that to the test so for the future it would give you more ground to refuse to see her. So yes to brunch.

But then again Bratty is Bratty and even on best behavior she will hound you for stuff and help, and you are on the spot. Therefore no to brunch.

So - thats my 2.5 cents.

Personally I would not attend as this is an opportunity for him to meet Bratty's Nutter GF and for him to catch up with her outside of weekly Zoom calls.  I would let him know that should she come your way again next time you can plan for a coffee date somewhere of your choosing to say hello should you be inclined.  Also I highly doubt your SO would get up and leave should Bratty make you upset...he would have to actually be paying attention and know what is upsetting you.

Admittedly, I'm torn.

With the Nutter GF, I agree that Bratty might likely be on her best behavior so I'd be tempted to go solely to see if she does. But I would drive my own car in case I needed to get up and walk out. And leave SO to find his own way home. *diablo*

Frankly, the situation is simply too iffy for me and - due to both Bratty's and your SO's past behavior (and his saying zilch), I would say NO. Make plans with a friend to have brunch, have a spa day, or stay home, relax, and pamper yourself. 

If it was me then I would not go. You are already anxious, Brattys history with you is poor. Why take the chance to put yourself in the line of fire and then worse DH lets you down because "he didnt notice". The usual excuse cause its safer for them than address poor behavior. Guranteed after you will end up in an argument if the likely scenario occurs. Is it worth it? 

OR go but change the restraunt . You need to eat at The Meat Eater Cafe (made that up lol).

Hun Bratty is not worth any mental gymnastics for you. You have come too far to go back. Has Bratty changed for the better? Wasnt it just a few weeks ago she wanted you to be a Tour Company for the nutters parents...like c'mon Bratty!!

Best of luck and blessings

Bratty has probably told Nutter all these horrible things about you, I would go and be super sweet and charming and prover her wrong.

Also if she invited you then it's her treat right?? Are Mimosas vegan?

After the Thanksgiving fiasco I'd never cook for Bratty again. But, this is in a restaurant and it's a meet girlfriend in-person event. So I'd go.

I'd go, put on a sickly sweet smile, find something I could eat on the menu, and stay mostly silent. I'd give nutter girlfriend such a good impression of me that she'd wonder about Bratty when she complained about me.

My GD married her wife last year.  I'm 76 so this was something new for me but hey, life changes and she's happy. But, altho I had met the wife,  M, before, I was surprised by their arrangement.  My GD who I always secretly considered a very major flake, handles all their finances!   She makes the major decisions!  They've bought a house!

My point is that this relationship might represent a change for Bratty.  You might be surprised.

I didn't read the responses, so sorry if this has been addressed, but does he need support to have brunch with his daughter?

I really don't see a need for you to go. He's having brunch with his daughter, not going in for surgery.

I'd come down with a hellish case of explosive diarrhea the morning of.  
 

 I Get wanting to test DH and see how he does but has he had any opportunity to pass the test since this all blew up?   Has he made any positive baby steps that would give you enough hope to attend?    More importantly, what if this whole thing blows up? Think of the worst outcome of this folly and ask yourself if you can survive it.  About those Disney passes, just shut that that down permanently. Tell her the truth (which might have her testing waters for years) or just tell her your source changed the rules for usage.  Anything to make her stop.  Yes a lie, but damn,  sometimes these crazy people need their demands shut down any way possible.  
 

I'd stay home if it was me and all this baggage was still hanging around.  Maybe your absence will send a loud message to SD and her father.   

DH has made good noises about not putting up with Bratty's disrepect. But, might he pull one from the secret DH playbook: I didn't hear her say that. I don't think she meant it that way. It wasn't a big deal.

Or, he might (reasonably or not) judge Bratty's infraction isn't worth all the drama of getting up and leaving a meal.

You and DH might develop a code word or signals or something to let him know that Bratty crossed a line with you. That would leave NOTHING to DH's imagination and no excuses. So, Bratty asks for Disney tickets again. DH acts like he doesn't hear her. You say (your code phrase) "DH did you get the laundry out of the dryer?" DH HAS to deal with Bratty at that point.

It's just too many "if's" for me. I equate your Bratty with DH's oldest daughter. Manipulative and underhanded. Not sure about your DH but I'd be very wary of mine holding to his word of confronting disrespect. My DH is very "unaware" of his kids' bad behaviors, even when pointed out. He also has a very difficult time of confronting any of his kids. And just a year and a half of being disengagement, in my opinion, is not enough time. 

You mentioned something about thinking this might be you holding on to a petty grudge. I strongly disagree. And having just finished a great study on forgiveness which a focus on not having to restore said relationships to forgive....I'd say you are holding on to wisdom and are using those facts to keep yourself safe. If DH's daughter invited me to a brunch for anything, I'd question the motive and remember her past actions towards me. If she's changed, she'd call/text/email/write me and say something to the effect, Hey, I know we've had a tough past. Can we start over." Anything to get the message across she's changing.

I'd just send my greetings through DH and enjoy my down time. Bratty needs to see you mean business and aren't even interested in meeting her GF.

Ugh. No I wouldn't go.

Period.

It will be awkward and completely unenjoyable.

Nope.

My vote is no. You are already feeling some type of way about all of this - you are going to be all  queued up and ready to jump out of your skin if she does act Bratty. 

Also, just because her girlfriend is going to be there, does not mean she will "be on her best behavior". Honestly, she might be WORSE. AND with "support". After all...they are a couple. I am sure Bratty's version of you and the relationship is MUCH different than reality. She likely has painted you as the wicked step-mother.