Section 20 of theDomestic Violence Act, 2005 can help your sister ,the section is meant to ameliorate the financial condition of the aggrieved person, who may suddenly find herself to be without a hearth and home. Financially, the aggrieved person may exist in a suspended animation, if she is neither supported by the husband, nor by her parents. In order to protect women from such a pergutory, Section 20 bestows a right to seek monetary relief in the form of compensation and maintenance. Section 20, thus, is a powerful tool for ensuring gender equality in economic terms. Section 20, does not contain any exception in favour of the husband. In fact, it recognises the moral and legal duty of the husband to maintain the wife.
So your sister may file petition under DV act or crpc 125 for getting maintenance. If his parents are here try for amicable settlement .