How about the beginning of a compromise. With the aim of working towards a more cohesive family where the siblings know each other and you do family stuff together?
Step 1. Every second weekend from now until Christmas DH and DD1 stay at grandparents but you meet up on Saturday and do a family activity together (keep it short to start with but super fun to distract the kids and keep them all occupied).
Step 2. Half way through the term the grandparents start "hosting" (ie at their place but everyone contributes to the meal) a friday night or Sunday lunch style meal. Once again make it super fun - involve the kids in the making of the meal (dad can make a dish with dd1, you can make a dish with dd2&3) . Make sure the meal involves kids favourites where possible. Then play a fun game afterwards. Only give compliments towards your dsd. Eg, cooking, lovely manners, pretty smile ( anything).
Step 3
The lead up to Christmas.
Your dh takes dd1 Christmas shopping for ( small) presents she can gift to her siblings. And then he takes dd2 &3 shopping for a gift for their sister.
You do some "family" type christmas things together in the lead up ( covid permitting) eg, santa photo, gingerbread houses, making Christmas decorations, putting up the tree ( your house and grandparents ( win, win), ice skating, Christmas lights drive with snack stop. This activities must be seen to be organised by DH and he needs to be enthusiastic and the driving force. You just need to be warm, supportive and enthusiastic towards everything. Fake it until you make it. Channel actress of the year if you have to. I'd suggest that any ruffles or misbehaviour from any of the kids is handled by Dad.
Step 5. Christmas
The new habits should be well worn in by now.
Christmas eve. Together at the grandparents. Do a family meal, watch a smaltzy family Christmas movie all together, make a "special" Christmas snack or dessert to have with the movie. You head home. The next day your house hosts lunch DH and dd1 arrive early to help. Grandparents can rock up at meal time. Lovely meal is had- DH gives a toast at the meal about how lovely it is to have all his daughter's together. Heap praise on DD1 for the time and effort she's put in learning how to be a big sister, very proud etc. After lunch gift giving- you give a special gift to DD1. Say youve really enjoyed getting to know her better and thank her for something she's been doing well.
Step 6. If Christmas day goes well. Invite dd1 and Dh to stay over at home. Grandparents go home alone.
Step 7. Make overnight invitations more and more regular until it's at least 1 night of each weekend ( set dd1 up with her own space in the house by this point) .
Step 7 - book a family holiday ( with the grandparents if you think it's needed) have lots of fun . Then after this start making both nights staying yours.
You've gor to start doing something. Even baby steps like this will make some progress. Then hopefully by the time it's DHs turn for Christmas again then she'll be staying with you not the grandparents anymore.
Best of luck!
(And yes I've had first-hand experience with step kids and an antagonistic exwife. Court helps but so will this. The "Carrot and stick" approach is needed when dealing with stubborn exs. The court is the "stick" NOT an actual stick. 😉