I had my last child in my forties and it was a lot more tiring than the ones I had in my early 30s. I can't imagine having to work a full time job (if that's what this grandma is doing) and then caring for a teeny baby during your rest days.

It sounds like this isn't just an occasional babysitting stint here, but a scheduled shift. If other family members are so keen that the single mom should be supported, they need to step up too.