How do you know when it is time to consider Nursing Home Care for your loved one?

I moved my parents into my home 5 years ago. My dad died last year and my mom continues to live with me. At 91 her health is declining. She was recently hospitalized with a bad upper respiratory virus and bronchitis and lost some ground. About 2 weeks later I was contemplating nursing home care for her because she had lost the little bit of independence that she had. Since then ( mid October) she has gotten somewhat stronger or at least is back to her pre-hospital self. She struggles with mobility and walks with a walker. She is incontinent off and on. She is forgetful. She needs help with dressing, and bathing. I pretty much do everything for her. I have an aide for 15 hours a week which allows me to visit and care for my grandchildren. At 66, I have a part time job which I can do from my home. I am an only child and without any family support. I am married but my husband is not helpful. At this point I am exhausted physically and mentally. I long to be free of responsibility. I want to be able to live my life without having to plan everything I do and make arrangements for my mom if I go out.

The issue is that she will be devastated and I don't feel like I have good enough reason to move her to a SNF at this point. She is very sweet and grateful and very dependent and attached to me. I would like to be able to care for her until she dies as I was able to do that for my dad. But I am running out of steam.

How have you made this decision? My guilt about moving her seems to trump my need to be free. I feel like I am waiting for a sign that will show me the way.