Is it permissible to offer the fidyah for a wife not fasting Ramadan for five years due to diabetes requiring insulin, and to give it to her poor and indebted mother?

Your wife must feed a needy person for every day she did not fast since reaching the age of puberty. She also owes expiation of feeding one needy person for each day she broke her fast and delayed making it up until the next Ramadan began. Her daughter may pay the expiation on behalf of her mother if the mother is in debt and in need, and if her maintenance is not obligatory upon the daughter.