I will concede that involving Facebook seems a bit crass. I do think she's telling the truth about peeing INTO the cup, but I have no way in which to gauge her intent. It could be someone who intentionally set about this scenario or it could be someone with a genuine medical condition who didn't expect that situation to occur at which point she must have felt horrendously embarrassed.
Regardless, what I've never understood is why it's safe for the FA's to walk around when the seatbelt light is on, but not the passengers.