When is it time?

MIL is 83 she is in very good health. She can walk and is relatively steady on her feet. She says she can hear us, but she doesn't understand what we are saying. MIL has a "functional" dementia. She has a very strict routine, if that is changed in any way-she is lost. She often showcases that makes it seem as if she is still sharp, but as her caregiver I know better. MIL lives alone. I bath her, prepare her meals (diabetes). I manage her home ,finances, shopping, Dr. appointments, and acquisition of Rxs. I try to keep her socialized but she is not happy about it. She allows me to take her to Church on Sunday...no more. It's okay if the family is with her but she won't "tolerate" being left anywhere other than her home. Tolerate in this case is increased blood pressure, dizzy spells and elevated blood sugar numbers(stress related), it takes her a week to get back on track. She NEVER complains. She is wonderful. She used to work in a nursing home so she intimately rejects any concept related. In the past, after hospital stays she had to go to rehab to get her back on her feet. She didn't do well there. She didn't participate with the multiple activities and since neither had cable,only regular TV, she would just sit there and stare into space. She always perked up when I got there but the nurses mentioned her isolation in both cases. Living in her home is basically assisted living cause I assist her and she has a developed neighbor connection. For her it works. A major benefit to her home(unlike ours)is, it's a ranch (no steps).She is okay right now, but I don't want to wait for something bad to happen. When is it time?