Gpa giver says did not get money from sale of land by gpa holder

A person A gave the GPA for her land to B in the year 1999. GPA was registered and it clearly mentioned that B can sell the land and do anything with it. After fifteen days, B sold the land to his mother C for approx. 2 lac rupees. A still owned some remaining land next to the land sold. In the year 2016, C filed a case against A because of some boundary dispute with A. Now A has given a counter claim that she gave GPA only for a small part of the land, and she did not get any money from the sale of land by B to C. Only to divert from the boundary dispute, A is making false claims to complicate the case. I have registered GPA given by A to B. What documents can i use against A? Is there any judgement by supreme court which i can give to my lawyer for assistance?