The position of law is that the properties left behind by a deceased shall devolve equally on all the legal heirs if the deceased is reported to have died intestate.
Thus the house property, if t\registered on both the names i.e., deceased aunt and her daughter, then your deceased aunt has 50% share in that property. Out of that her own daughter in the capacity of her daughter and legal heir shall be entitled to 50% share in the share of her mother in that property.
If that property was bought on your aunt's name alone, then this entire property shall be shared by her legal heirs, i.e., by her daughter and the legal heirs of her predeceased son, thus your aunt's daughter can have 50% hare in that house property.
The above is irrespective of the property already given as gift to the daughter by her mother earlier.
This has nothing to do with the share in the intestate property.
If no amicable solution is arrived then the solution can be had only through court of law by filing a partition suit.