I feel she was imprisoned or convicted of some crime, maybe her husband wanted to kill CA as she was a girl and in a bid to protect her she ended up killing him as a result of which she ended up in jail. That could explain why her past isn't public and she isn't revealing much about herself.
I want her past to be very sympathetic so it can be a slap on Anuj's face for all the accusations and taunts he had been directing towards her.