Hard landings are generally pilot error. It is possible that wind shear could cause/contribute to a firm landing though.
Of course if it was an autoland that was firm, then it would be a mechanical issue. But if you had a firm autoland, the pilot should write it up and not use it again until it is "repaired"
AA flight attendants can call in sick if they don't feel healthy enough to safely do their job.
It is their discretion - and an FAA regulation that you not fly (work) when sick or injured.