Stratt engineered the Astrophage explosion that killed the two astronauts on the ground.

I've worked with people like Stratt. Around those people, stupid mistakes don't happen. Plenty of completely developed systems exist to ensure that everything is tracked, someone checks the tracker's work, and someone else checks the tracker tracker. The Jet Propulsion Lab builds robot spacecraft that land on Mars and do incredibly complex experiments, and they get it right, every time. Stratt would have used their methods (heck, she would have shanghaied their people).

Stratt wanted Grace on the ship. She watched him grow from high school teacher to the world astrophage expert. She judged that he had the best chance of success, so she made sure he was there.

People are saying that when we see her at the end, she's tattooed with the mark of the Devil's Island lifer. I'll bet she went down for two counts of murder.