Transfer of flat in the name of widow

As per your statement : 1. The flat in the cooperative housing society was in the name of your brother. 2. Hence as per Cooperative Societies Acts and Rules your brother was the Registered Member of the society and was issued Share Certificate too. 3. Your sister in law was the Nominee. 4. As per Cooperative Societies Acts and Rules the Managing Committee of RWA has to transfer the flat and Share Certificate both in the name of your sister in law. 5. The Managing Committee or the RWA is bound to do it. 

Download the state cooperative housing societies acts and rules which are very crystal clear on such issue.

Your sister in law is the sole legal heir to her deceased husband. Hence automatically she will be entitled to inherit the entire property. 

She can obtain a legal heirship certificate and get the revenue records of the property to her name and then she can apply for transfer of share certificate of the apartment to her name.