First of all if it was an ancestral property, your mother can claim a share in it only after the latest amendment act came into effect.
In Tamilnadu the amendment came into effect in the year 1989 hence she may be eligible for a share in the0 ancestral property as a coparcener provided that the property in question still remained as ancestral property during the latest amendment to the Hindu Succession Act in the year 1989.
If the properties remained unpartitioned right from the purchase by three generations before her and has fallen into her generation as undivided all along, then she may be considered as a coparcener in the ancestral property after the year 1989, however she should have not been married prior to that year.
There are many more details to be ascertained in this regard hence it would be better to consult a local lawyer with all relevant papers for proper advise and further action .