Opinions needed, how old is "too old" to cook an entire Thanksgiving meal alone?

Hi all, Mom, 73, degenerative disk disease in neck, lower back, mild heart valve leak, colitis, expected to cook Thanksgiving meal, (by herself, no other cooks to help), for my Stepfather, his brother, his nephew, and the nephew's new girlfriend.

She had a TIA a few years ago when my niece, her kid, and her boyfriend came for their birthdays. Guess several days of cooking, baking separate cakes, wrapping was too much. Lady up the street died making Easter dinner for her grandkids a few years ago, so I am kind of nervous about this.

They used to go out for buffet for Thanksgiving, when I lived way out of state. Then Stepfather decided he wanted left overs, got her to make him turkey breast, potatoes and gravy, pie, for him to take to work for a few days every year after guests left.

I moved here a few years ago, 3 years ago I told him I thought it was too much on her and we should go back to the buffet tradition. No go, but said just one last one. I agreed. Last year, reneged on his agreement, said he wouldn't get any left overs if we went out. I told him he knew full well she was too old, he said he'd cater it, which he did. Mom begged me to come help, and bring other things too, (I had other plans elsewhere), said she plain couldn't do it, so I caved. She was right in that they didn't have enough food from the cater purchase, was surprised how small the portions were for the cost, and I also was surprised how much work it still was for her to get all the stuff ready. I took bird, giblet gravy, potatoes, stuffing that I made at home. THAT was supposed to be the last year. This year he announced once again he'd invited everyone to their house for the dinner. I flat said NO, and I'll have no part of it, my husband and myself are going out to a buffet, (which we never have done, but I've got it by myself for 32 years when we lived in a different state and I'd like a break myself).

Have stuck to my guns hoping they'd change their mind and go out with us. No go. As a matter of fact, he went from going to cater her part again, to now she's getting it from scratch since I'm not participating, he's afraid there won't be enough left overs for him to gore for 3 days. Ugh. I am worried. I don't want her to have another stroke, or worse. Most days that I go see her for an hour in the afternoon she's on no sleep, (chronic pain keeps her awake), she's often confused and has a lot of trouble just getting a cup of coffee made from their little single serving deal they've had for years. Am I wrong? How old is "too old" for this?