My daughter-in-law is hooked up to oxygen 24/7. It doesn't stop her from being a school teacher, nor from traveling to visit us.
My first wife (God rest her soul) was hooked up to ambulatory dialysis 24/7. She lived a fairly good life that way for the five years until her death.
I hope your MIL fares as well.
It will be interesting to see if her will to live continues to be as strong as it has been before. I think people do have a bit of control over it. I think it's acceptable to pray for death if it be his will. Not that I would pray for her death, but maybe if I were in that situation. It's interesting to ponder.
We knew this yesterday. They will break the news today. Not sure if this means back to her assisted living or to the nursing home. It's odd to watch this progression and yet it will come for us all if we live long enough.