Open question: Problem with me and my mother both on the house!?

I and mine bought a house nearly 2 years however straight ago my name is shes on the letter and the Pfandbriefdarlehen, on the letter however that. I would like to shift and receive my own house out. She says that she cannot sell, because there is no cheapness in the house. But it should not give after 2 years? And could I buy it perhaps out? How did this work become exactly?