Under the Hindu Adoptions and Maintenance Act, 1956, the widow of a son is a dependant:

Section 21(vii) lists "any widow of his son or of a son of his predeceased son, so long as she does not remarry", provided and to the extent she is unable to obtain maintenance from her husband's estate, or from her son or daughter or his or her estate, and, for a grandson's widow, also from her father-in-law's estate. Remarriage ends her status, and living with her in-laws is not required.