Mine has been an arse about Christmas too. I think she was game playing because I'd invited her to ours rather than trailing a toddler and small child down to theirs.
I'd explained there was a fully accessible modern hotel about 15 minutes walk away, tops, and the walk was accessible on a mobility scooter too.
She then booked a B&B and then cancelled it because it was up stairs, booked another hotel and cancelled it because it wasn't suitable, then finally booked the accessible hotel.
There was then a big performance about whether or not the accessible hotel was suitable so I went up and walked around it and told her it was. She didn't want to "muck me about" apparently.
Lo and behold, a few days before Christmas, once I'd ordered all the food, DF became "too ill" to travel.
Like an absolute mug I took my family down on Christmas Eve. DF was not any more ill than normal at that point.
I'd taken some food down which "D"M moaned about. She didn't apologise or offer to cover any of the extra food or our rail tickets or anything.
Then they went on holiday a week later.
Looking back I'm really annoyed at myself for going, but it was all set up like DF was going to die imminently so we all had to jump - she did that a lot back then.