I agree with that, but once someone IS employed by a company, they shouldn't have to worry about losing their job because of what they do on their OWN personal time. Unless there was something specifically addressing something like this as cause for termination or it was something in her contract with the company, then at most, she should get a warning, and if that isn't the real reason they fired her, then somebody needs to have the guts to tell her what the real reason is.
"She posed for a cheesecake photo in what her employer considered to be an inappropriate way while wearing her employer's uniform."
Not all people automatically know what an employer might consider inappropriate. If she was not given a given a warning, her termination is at the very least, unfair.
It sure looks like she was on the clock when the cheesecake photo in question was taken. Unless she built a full mockup on her own dime of the passenger compartment of an aircraft at her home (which is unlikely), she was wearing the employer's uniform and presumably aboard one of the company's aircraft.
Last time I checked, Texas (her putative place of employment) is an "at-will" employment state. Except for very narrowly-defined criteria such as racial discrimination, an employer can let you go for cause, because they're having trouble meeting payroll, or because you wore brown pants to work on a particular day. There simply is no "right" to employment.
There is language in all airlines governing behavior while in uniform and she knew damn well that cheesecake pose in uniform would be cause for termination. No industry has more stringent guidelines for behavior on/off duty than the airlines.