Is it OK to have your Mother watch your children (40+ hours per week/5 days per week) without pay?

Jenni & Keith both work/make about $100,00 yearly. Jenni has her widowed 67 year old Mother (Gramma) watch her 2 year old daily as well as 8 and 10 year old boys in summer. She has been doing this for past two years becausea it was a comfort to her upon her husbands death. She had loved ones around her all the time and she felt needed. Gramma carts children to school, dentist, activities, etc and does all things a nanny or the children's parents should be doing. The Gramma is retired and on Socl. Security. She is on a VERY limited budget. She lives in her own home. Jenni does not pay her Mother for childcare and this is a hot topic in our family! Jenni compensates Gramma for gas and sometimes buys food. Gramma complains to other family members that she must pay for food, activities for kids (waterparks), car repairs, etc... She doesn't have any discretionary income for herself nor time to start her life. She is unable to save $ and unable to save $ for a new car. Gramma wants to start dating/traveling again but does not have time nor $. She complains that she doesn't have $$ to buy a few lunches/dinners during her dating process. She desperately wants a man in her life again. She does not want to disappoint Jenni and is not strong enough to ask for $$. Jenni gives her a purpose in life and makes her feel needed. Jenni feels that a Mother is supposed to do this for free. Jenni/Keith drive nice cars and have nice things. Gramma does not. HOT TOPIC: Gramma has opportunity to take a vacation and Jenni/Keith refused to pay for her plane ticket. Another relative feels that they are taking advantage of Mother. This relative feels that this is the least that they can do. Jenni/Keith feel that Mother is doing this for free for the love of her grandchildren. I thought that Gramma should just give up the free daycare and get a part time job. She could still see the kids a day a week. She should pursue finding a man to spend the rest of her life with and think of herself first. She is not getting any younger. Grandma does not listen to me. What is one to do in a situation like this?