About void marriage and customary divorce

Hi sir my relative is hindu she was married forcely at age of 13 with her relative on 1978 later only she came to know her husband was already married and he live with first wife .she inform to her mom within a year my relatives approach customary divorce to panchayat ,they were separated by panchayat. Later 10 years at her age of 24 a person married her he know all past things and accept her and begot childrens. Now her second married husband passed away for to get legal heir certificate they her as his wife because of her first child happened,they not accept panchayatdivorce. My quetion is her marriage annullment at a time of marriage because her first marriage is bigamy her first husband hide the truth of his living first wife and her marriage happen at age of 13. By law her first marriage is void is it necessary to get divorce by court she got divorce by customary panchayat. Could she have chance to get legal heircertificate of her second married husband as a wife.pls reply me .