OP, I’ve lost track of comments, but whoever advised you not to rock the boat because you never know how long your mother has left is slathering you with emotional blackmail.
You yourself deserve consideration now, as (forgive me, but I am much older, so I’ve a licence to blurt!) you are no chicken either.
Think about this, if emotional pressure is the way all this is going.
Say you change nothing, and your mother passes away within five years (God forbid).
There’s every chance you will have a solid, festering resentment inside by then, and with good reason, and this will definitely taint your memories of her.
I think now is the perfect time to ensure your loving relationship is refreshed and perhaps pruned a little.
(I’m blathering in like this because my mother’s final years, vis à vis me, or vice versa, could have been brighter and happier, more honest; and this is very hard to have lurking behind my memories of the dear old thing)
Far better upset the apple cart now, use a bit of kindly firmness if necessary but do not agree to be steamrollered any more.
Standing up to the weight of ten years’ habituation might seem daunting but in reality, it doesnt make your case weaker does it? It makes it stronger!
You have no more available money or chunks of time and energy to give (and that need not be explained in detail, unless DM is not very bright) so Christmas absolutely must change, for the two of you.
So what? It’s a change trivial in the extreme, when you are proposing a lovely snug family celebration at your house now, and how nice DSis will be home too! Old people cope with altered circs a lot better than their reputation insists.
When the alteration is necessary because the always reliable person badly needs the change, it’s pretty well unarguable for anyone decent.
With that in mind, be ready to keep up your end and don’t shift from Christmas at yours.
The change could be revivifying for both of you.
But if (horror alert) this comes to pass, but on Dec 27th DM has a fall or worse, it would be nothing at all to do with you, in terms of more guilt.
Please, please, stand up for yourself. You have the right to exist as much as anyone but are trying very hard to take up only half your allotted space. A dutiful daughter need not be entirely self-abnegating.
Who knows how many Christmases any of us has left?
Resolve to enjoy them rather more to your own taste now; it’s high time.
/rant ends
[The pp who knew of an old chap who died after not getting his way at Christmas knows very well that it does not constitute a parable to guide us.]