I believe it's her real, biological mom.
I'm guessing that the exact cause of death is not known. She had long term medical problems, so there may be some question as to which medical problem caused the death. Maybe if there is a question of a medical misadventure, that complicates the issue.
Does anyone know if they will hold off issuing a death certificate when someone has been pronounced dead, but the cause is still under investigation? In Texas?