If she is not dead, let them pull the plug on the machines propping her up.
If she is truly not brain dead (and it has happened that they have prepared to take supposedly brain-dead people's organs only for them to wake up), she will respond.
If she is truly brain dead, she will die.
I empathize for the woman's family, but this is, quite literally, do or die time. No amount of propping up what is basically a corpse is going to help this woman recover.
They'd be best advised to start looking for a lawyer and investigating a wrongful death suit.