Two things the autopsy would be keyed on, one would be evidence of smoke inhalation in the lung tissue, which would be free of it if she died before the fire (Not necessarily foul play, could be a heart attack, a self-administered drug overdose (Intentional or not), a drug reaction, etc. If the lung tissue appears consistent with death in the fire, they may not do toxicology, but that is the other main thing. Of course they will also look for things like fractures from blunt force trauma, wounds, coronary artery damage that would explain sudden death, all the normal things of that sort.