M.M.
I'm in the same boat. Except my father in law had a massive heart attack then a major stroke and minor stroke, which has left him unable to speak or communicate in any way, and a portion of his body is paralyzed. My mother in law had to quit her job and now stays home with him at all times.
She needs someone to talk to, to vent to. She lost the man she loves in a sense and she is lost with how to go on with life as it is.
One thing you need to find out is how her finances are going. We quickly found out that my mother in law was supporting themselves by living on credit cards because she knew no other way. She had never handled the family finances. She knew nothing about their future retirement plans or how to go about anything financially. That was a tremendous burden that we came along side her with.
The other thing would be to insist that she get away by herself every now and then. She needs time to breath away from the situation. We try to go over and stay with my husbands dad twice a month so she can go grocery shopping or do anything to get out for a few hours. Sometimes I take her shopping at the mall or go to other special events or other places, even out to eat, while my husband stays with his dad. She needs the break, she may insist she doesn't but she does. My mother in law always feels guilty when we go, but it always puts a smile back on her face.
If she doesn't have a best friend that she can cry on their shoulder, I encourage you to be that person. There have been many evenings where I'll go over to my mother in laws and we'll sit on her porch and she'll just let it out, after he's gone to bed. She plays so strong for so long, but she has to break eventually. I can't imagine walking in their shoes, the men they've depended on are leaving them helpless and in a position where they have to make all decisions and handle all problems. It's not their fault, but it's an extremely exhausting and an unrewarding job. There is no positive hope for the future only harder times. Please let me know if you need to talk. I can try to help.