We had a similar thing when DS was nearly 2. Off season. DM booked us all a week away in her favourite hotel abroad, geared at pensioners. Generous, but she didn’t even ask if it would work or if we wanted to go.
The only way to leave the hotel was by timetabled bus (walking down the narrow mountain road with no pavement and lots of bends with the buggy wouldn’t be safe). Half-board, and dinner was served at 7pm, sometimes 7:30. DS went to bed at 6pm. Parents changed their room for a better view(!), meaning it was out of range of the baby monitor. One of us therefore had to stay in a darkened room with DS every evening, rather than spending the evening together.
Breakfast from 08:00. DS woke at 06:00.
It was freezing cold (October), so the pool was out of bounds. Very little outdoor space otherwise.
She did offer to look after DS for a day. Without us, she couldn’t manage to leave the hotel with him. After that day, with a starving, very active child, who hadn’t had his 2 naps (we came back close to midnight), she has never, ever tried that again.
It my case, DM tends to be a rigid thinker: ‘that’s how I see/imagine it, so that’s the only way to see/imagine it’.
Maybe your mum needs a clear warning how the weekend will be then has to experience it for herself?