I married my wife over ten years ago and her Mom lived with her then. She is a wonderful woman; they both are, but Mom's needs have increased over time; she is 85 and needs someone with her round the clock, she has 'age-appropriate' short-term memory loss, walks with a rolling walker and will need an electric cart soon. My wife rarely works her small business, we have no retirement savings (we are 51), our life revolves around caring for her Mom--our life is on hold. We've recently got my wife's brother and sister to help 'coverage' and have started to get my wife some balance in her life, but even scheduling a short visit to a friends house for dinner has become a HUGE DEAL. If Mom lives to be 95 (and we hope she lives that long), we will be 60 with no retirement and will have spent our better years running an assisted-living center. Im at my sits end.
I don't know enough about the situation to have a feel for what should change. Why does MIL need 24-hour supervision? "Age-appropriate" memory loss (whatever that is) and needing a walker does not fully explain that. Why can't you go out for a few hours in the evening and leave her alone? My 92 year-old mother has mild cognitive impairment and needs a walker. She lives alone in a senior apartment. She gets a lot of support both from agencies and from family, but she spends large portions of each day alone. I am certainly not saying that your MIL could do that, but it would be helpful to know what impairments make it necessary for 24/7 coverage.
Would you be willing to provide some additional information about MIL's health? That might inspire some more specifically helpful responses. Can she use the bathroom on her own? Feed herself? Use a phone? Understand how to use a medical alert device?