Legal advice on ancestral property

I need a legal advice on ancestral property. My father's first wife died when her daughter was around 5 years age then after my father married my mother, I am only son. My father and mother took care of us and her marriage was done when I was young and all marriage responsibilities were taken care. My mother had to sell most her gold she got from her parents for my step sisters marriage. My father was died in 1987 when I was in 5th grade. After that mother took of care me and my step sister. My step sister was given all required gifts during every year for festivals and expensive gold gifts for her daughters marriages. My mother had to sell most of agricultural land for her health related expenses and my upbringing and education. Now we are left with 3 acres of ancestral property and one old house in village. My step sister claims right on property 30 years after my fathers death and she sent legal notice to my 70 years old mother and me. I want to know legality of this claim as she was given all marriage related gifts and every year festival related traditional gifts in last 40 years since her marriage. I read about 2005 Supreme Court judgement on Hindu Family's property rights claims by daughter after marriage. If my father died before 2005, does my step sister's claim is valid. If yes, is she also not responsible for my mothers expenses since last 30 years of my fathers death. I need legal advice in this regard, whether she has right or not?