No one has answered the actual "relationship" between the maker and her grandmother-in-law.
Just because someone happens to have a blood tie to one, doesn't make that person near and dear.
I think it is fair to charge for materials/out of pocket expenses -
I paid my son for remodeling work - not as much as he would have gotten from others - but roughly I paid him about two hours of my salary for one hour of his work at the time. Plus the cost of materials. And he was learning at the time.