Do you have a good relationship with your dil? It sounds like you want to help on your son's behalf and if you can afford to help I would in other ways other than giving her money. I agree with the others, groceries, clothes, etc. Maybe her parents are helping her also. Did you ever think of paying for some of the daycare so she could work full time?
Sounds like your son is trying hard..........Blessings on your family.
Lo