Before the flight, Michelle and another flight attendant, JD, assisted Locke onto the plane when the special wheelchair for loading disabled passengers was missing. Later, she was at the entrance to the plane when the other passengers were boarding. ("Exodus, Part 2")
During the flight, Michelle was serving drinks to the passengers, two of whom were US Marshal Edward Mars and his prisoner, Kate Austen. When she asked the Marshal what he’d like, she seemed unhappy when he asked for black coffee, most likely because he called her "sweetheart." She went to the tail section to make the coffee for Edward Mars. ("Pilot, Part 2")
A few minutes later, the tail section separated from the rest of the plane; Michelle was killed during the crash.