The subject property though inherited by your grandfather from his father, i.e., your great grandfather cannot be an ancestral property to your mother.
It becomes your grandfather's own and absolute property. In that your grandfather has full rights to dispose it n any manner as he proposes to or desires about.
Even if it can be considered as ancestral, your mother who died in the year 1993 cannot have coparcenary rights in it because the law giving equal right for the daughters as coparcenary was amended on in the year 2005, therefore your mother did not have any rights in the property at the time of her death.
In view of the above paragraph, since your mother has not left behind any property or rights or interests in any property during her death, you do not have any right to claim a share in the capacity of a legal heir to the deceased coparcener.
The property is certainly not an ancestral property to you. the rights if any, arising out of ancestral properties shall extinguish with your mother alone and since she is also not a coparcener, there is nothing to claim as a share in the property.
If you suspect the Will or gift deed or whatever deed by which your maternal aunt got the property transferred on her name, as a legal heir to your mother you can challenge the same by filing a partition suit and questioning the validity of the alleged transfer of property. Success rate is very less.