If you bundle up you can still go out for walks! Maybe not an hour if you're not used to the cold though.

So you can aim for it like... 30 minutes when she gets home.... and as long of a walk as you can stomach in the weather... and maybe one Christmas movie tops (hell, invite them to watch it with you. Movies can at least be endured in relative silence and can count as a "family" activity)... I'm sure your mom would complain/criticize you over cooking, but do you think you could offer to make supper at least a few times? Then you could have the kitchen solo (unless your mom would hover over you... which case that wouldn't help). Could you spend some time each night doing chores at home? Boring and tedious, but it counts as a "dutiful daughter" thing, and again, as long as she doesn't follow you around, will give you time to hide a bit. Time your showers for at night when they're still awake. If you can sleep in until she leaves for work that would help then - although she might wake you up? In that case, hopefully it wouldn't last for long.

Is your T planning on doing any phone sessions with you during the three weeks? If so - time them for at night and pre-plan topics that you could endure your mom catching snippits of it. Have your T tell her that to have a session you need privacy. If your mom can't handle that then it'll be scrapped, but your T can duke it out with her for a little bit if she's up for that? (This obviously won't be possible during your T's holiday time). Can you get ahold of any workout videos? If so, spend half an hour each night working out. You could probably borrow one from someone for the three weeks.