Can a widow make a will for her husbands partitioned HUF property

Sir, My grandfather are five brothers and they all amicable partitioned their family property through civil court in a family settlement. My grandfather has four sons and out of his share through civil court family settlement he gave 1/5 share to all keeping 1/5 share by himself for survival ship of him and and her wife i.e. my grandmother. Through the rental earning of his share my grandfather and my grandmother carries out their living without taking help of any sons. In 2005 my grandfather died intestate (without writing a will of his 1/5 portion), my grandmother used to maintain and got all rental earnings by herself for survival, in the meanwhile my father and 2 uncles died and I( grandson used to take care of my grandmother). In 2011 my grandmother wrote a will regarding the 1/5 portion she inherited from his husband. My grandmother died in the year 2021, now my remaining 1 uncle is challenging the will written by my grandmother, stating that she has no power to write will of 1/5 portion. Please guide