Illegal transfer of ownership of MHADA flat to family member

My father owns flat in Mumbai suburbs since 1970's.He gave it to his brother and his wife to stay in 80's. His brother died and since then his wife(widow) stayed there. They donot have any children.My father let her stay in good faith & sympathy. After few years she requested my father to transfer the flat to her, to which my parents denied however they allowed her to stay on the condition that she doesn't get married. Now it's been almost 40 years that she stayed there. 2 years ago we realised that she transferred the ownership to her name illegally I.e without my father's consent or any NOC. I approached MHADA to get the true certified copy of all the property documents by filing RTI to see if at all there was any kindly of document used for name transfer . But to my surprise, there is no NOC or no sale agreements or not a single signature of my father stating to transfer the flat on her name. She has filed an application to MHADA to transfer the ownership and it was granted without my father( original owner) permission/ consent. What should I do? Can we claim back the property? Can she retain the ownership on ground of adverse possession law?