Is a non-working wife who has a small amount of money given to her monthly by her husband obligated, by Sharia, to spend on her mother, or is that considered an act of charity for her?

The obligation of financial support for relatives is contingent upon the need of the recipient and the financial capacity of the provider. Therefore, it is obligatory for children, both male and female, to provide financial support for their needy mother if they are financially capable. This support should cover her needs for food, clothing, and shelter, provided that the financial contribution is in excess of the provider's own needs. If the mother is not in need, then what is given to her is considered a gift and a commendable act of kinship. All children share in the responsibility of providing for their needy mother according to their financial means, and the mother has the right to demand her financial support if they fall short. A daughter who provides for her mother is rewarded in all cases; either for fulfilling an obligation, or as charity and an act of kinship if the financial support was not obligatory upon her.