Section 21(vii) in The Hindu Adoptions And Maintenance Act, 1956
(vii)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 that she is unable to obtain maintenance from her husband’s estate, or from her son or daughter, if any, or his or her estate; or in the case of a grandson’s widow, also from her father-in-law’s estate;
