ancestral property and how yo get the share

Hello.. There is an ancestral property of my mother's side...she has no brother...Her father died 13 years back and mother 2 months back...Now my mother's real sister wants to sell the house and keep all to herself..She is saying that property has been transferred to their mother's name and she had given her power before death to do what she wants..She is claiming that she had the papers..But we checked in the corporation and there it is coming that property is in the name of my mother's great grand father and grand father...We don't understand how she is saying that house has been transferred to their mother's name??? And how can my mother get her share???