What was keeping her from sliding the deadbolt back and walking out the door?
“Deadbolt” may sound sinister to someone unfamiliar with locks - but it is actually the easiest type of lock to open, by far. There’s no key or combination or anything - you just slide it open.
There’s got to be more to this story.
Not only that, if she was alarmed about the captain’s behavior, why didn’t she open the door, get the flight attendants to remove the captain from the cockpit, declare an emergency due to the captain having some kind of mental breakdown, and land at the nearest airport?