Don't be so hard on the f/a in the back. She had a completely different perspective on what was happening. And when Joe Passenger decided to run past her and get the back exit open, and let water in, I am sure that didn't help. Everyone reacts differently to situations anyway. She did her job, got the folks in the back to safety, and deserves that credit.
"Serious injury" is defined by the FAA as "Any injury which: (1) requires hospitalization for more than 48 hours, commencing within 7 days from the date the injury was received; (2) results in a fracture of any bone (except simple fractures of fingers, toes, or nose); (3) causes severe hemorrhages, nerve, muscle, or tendon damage; (4) involves any internal organ; or (5) involves second or third degree burns, or any burns affecting more than 5 percent of the body surface."
It wasn't a term she made up to get workman's comp.