In answer to your question, she is undoubtedly a mug, but feels she is being a good mother.
You won't alter her. She has done it for the past 50 years and her daughter and partner have no compunction about letting her, probably saying, mother loves doing it, and it wouldn't be the same if we did it.
I think your friend is finding it increasingly hard, but until she accepts she can't do it , nothing will happen.
And when it does, her daughter and partner will probably go on a cruise leaving her behind.
All you can do is listen and keep suggesting gently that she asks for help. But I doubt she will.
Sad.