I apologise for not coming back to this yesterday. Life got in the way.
It sounds like you have made your decision, and you are happy and it's a good one. You've listened to your DD and put her NEEDS ahead of your DPs feelings - well done. And your DD will feel supported and listened to, that her needs and feelings matter. That is soooo important.
For other visits, hopefully some of this can help.
We travel "down home" a reasonable amount. DD used to find it very stressful (and happily, now that her weekends are so busy with a couple of clubs, the numbers of weekends we can travel have reduced significantly).
She gets her own room, and almost always has that room. (When DFIL was ill last year, her room turned into the "sick room" with a hospital bed, even though DFIL only used it for 2 nights - it was kept in case he did come home again - DD had a camp bed in DPILs room for that period). #
She knows what's there - a small lamp is put up for her, and particular soft blankets over the duvet (DD sleeps between 2 fleeces at home and often pulls the softie in DMILs under the duvet). She brings her ipod with music, and earphones, from home, and a current book, and normally "Max" the star-covered build-a-bear for snuggles (who gets ignored at home but snuggled a lot while away). And she is allowed to go down to her room whenever she wants.
I don't bombard the itinerary with loads we "must" do - people to see, jobs to get done etc. I will have loads of things in my head that I'd like to accomplish, but I know I will get half of those done if I am lucky. I need to build in quiet time.
There are certain things we do everytime we visit - like a farmer's market that is held on Saturday mornings that we get a few things at (including DD having "second breakfast" of pepperoni pizza at 10am!).
We are also prepared to walk away with DD if need be, and give her quiet time by going for a walk or a drive.
At Christmas, we rent a cottage separate to the family homes - there is probably room to squeeze us in, but more squished than normal and both our houses are a lot more manic, so we need a quieter place to retreat to on occasion - DD will just about manage Christmas Day itself as she knows she will get back to the cottage and have a calm, quiet morning on her birthday. Last year, as there are so few cottages and w were late booking (and DMIL was still so upset that we dropped looking very quickly) - we ended up in DMIL's house, in very bad weather that meant no escaping, and DD had a very tough time. We ended up almost cancelling another 2 night trip, but cut it to a single night instead, that we always do on New Years', because of how bad Christmas itself was for DD.
The other thing is that on Christmas Day, we need to drive from 1 house after turkey lunch to the 2nd house for more presents and turkey dinner in the afternoon. We always take that chance for a SLOW drive, sometimes even going the "scenic route", to give all of us but mostly DD some peace and quiet time.
We used to always bring specific food with us - like a tin of spaghetii hoops etc - that we knew DD would eat. She can get fussy when over-stressed. She will eat reasonably well, but sometimes either needs to get fed and let slip away to bed/quiet time, or gets starving and there is no sign of the planned meals materializing, or she gets to a stage where she needs something she can control and that will be food (so even foods she would often accept, like Granny's soup, would not be allowed she MUST have the tin of spaghetti or whatever). It might be literally as simple as a tin of spaghetti - but it's easy to prepare and eat, and she knows it will be there if she does need it. There generally is a tin in both houses anyway, but for a while, it was important that we had one in our bags so it was definitely there if needed (lots of times it wasn't needed - but knowing it was there was important to DD). She's got better over the past couple of years at expressing herself in general so this is not so important now - but it wasn't about the spaghetti itself, it was as much about knowing that something she could control, and also that she had something that could solve part of the problem if she needed it to.
I am also always happy for DD to come and be involved with my chats rather than "off you go and play" - she's an only DC and the eldest DGC, and often was the only DC on 1 side (other DGCs live abroad) and not as interested in running and screeching as others could be. My DPs were not as keen to have her always around but have slowly realized that she will head off when she is comfortable. There is a big party we go to on our street - 1 set of neighbours invites the street and their expat friends so its chaotic, full of DCs having fun, music, noise, ....everything DD hated. The first year we went, she stayed on my knee the whole time nearly, not even playing with her BFF, but talked a bit with the adults, ate her way through the meal and then really impressed the French friends by devouring the cheeseboard, eventually slid off to play for a few minutes with the other DCs as they were getting a bit tired and slowing down - but did need to go home a little earlier than others. At this stage, and she knows everyone, she sticks like glue to me for about 10 minutes, then heads off to play but comes back a lot, and everyone there has always been happy to have her part of the adult group at the table when she slinks in for 5 minutes (sits on my knee or now often stands beside me having draped my hand around her shoulder, sneaks a few bits off my plate, has a small chat with the adults, and then heads off again once reassured).
In my DPs house, she is expected to get on with being a DC and not be "babied" at the table like that. She doesn't look to sit on my knee there, but does come over looking for a long hug. It's not attention seeking, as DM seems to think, its a need for reassurance. And when she gets that, she will often head off again and get involved with her own entertainment/other DCs if there/other DAunts and DUncles rather than sticking to me like glue. So its important that I pay attention to DD's cues, rather than pandering to DM thinking I am babying her (DD is almost 11) - when I used to listen to DM and push her away, we'd end up with proper meltdowns and DD getting a lot more "clingy".
Sorry, that may be a slightly confused post, but I hope it is a bit helpful - I am trying to give things that help me and DD, and also say well done to you, and especially your DD for expressing her feelings - THAT is SUCH a big step.