Did your DH not see this coming?
What provision did he and his mother make for her old age? What conversations did they have?
TBH, if I live to see 94 the wrench away from my home would be awful. Going from my home to my DS/DIL’s house would be enough, even if I had a dog and child to contented with. But I’d consider them both a price worth paying and of course (hopefully!) I’d love my DGS.
The thought of being farmed into a care home when I don’t need nursing would fill me with horror.
I don’t think that making adaptations (non-permanent) in your home is that big a deal. You don’t have to curtail your weekends etc. She manages alone right now, she can manage for a few nights here and there. Same as during the work day. She can live alone in her house. Once your dining room is adapted to her, she can live alone there.
Comparing the upheaval to you of upsetting your home furniture and it being a bit of a squeeze for a few years but having her surrounded by loving family till the end, versus the upheaval of putting a 94yo lone woman in a care home to be visited when you can - well, there’s no comparison. I’m also a firm believer in inter-generational living. It’s good for young children to be around the elderly.
I just don’t think I could do it. Like babies and toddlers, older people need not much: food, water, shelter, love. Life going on around them. It’s not much to ask.
Caveat to all of the above is that she lives by your rules. Obviously you adapt to suit her physical restrictions, but what you say goes. You’re in charge. And, the big caveat to all of this is whether there’s a bathroom downstairs or whether your friend would agree to a stairlift being installed (to be removed before you leave your tenancy).