OP I think you've worded it badly which is why people are giving you the responses they are.
Basically this is about your DP, and to a lesser extent about the fact that his mother has been rude to you.
So - for 20 years, you and your family have celebrated Xmas just fine. In the meantime, your H spent an amount of Xmas he was happy with allotted to his mother, but didn't put himself out unduly.
Now that you're married and he has someone else to pick up a certain amount of the hosting slack, suddenly he wants her there for the whole thing and it's mean and she's lonely if you don't plus he won't have to drive her around if you just let her stay
On top of that, she's been rude to your family before and so they don't really want her around.
You're already compromising WAY past 50-50 in my book and I'd tell your H to jog on. So it was just fine to limit her visit when he'd be the one put out, but with you presumably changing the beds and soaking up a lot of the entertainment ohhhhh we can't leave her on her own. No thanks - add on top of that the fact that you've got your own family that you at least want to have some clear family-only time with rather than completely indulge a person who's only been in your family two years... it's a no brainer.
Tell him you're changing the plans completely - if MIL can't be alone all of a sudden, you'll have a meal with him and your family Xmas eve then pack him off to MIL's for the day and night 25-26th.
I'd bet that suddenly she'd be perfectly capable of being alone again!