The most sage advice you can give anyone.
Don’t post anything on the Internet that you don’t want your boss to read.
Good advice. I always think of whether I'd want my grandmother to see me say something. Same sort of thing. Some good advice for email, too, is if you mention anyone by name you should cc: them on the message. If you can't or won't cc them then re-word it until you could. You can trust that it'll find its way to them anyway.
Also... Never, ever, hit "send" after the second drink. Just don't. It'll wait, and you'll be very glad in the morning. :-).
As a boss I would not fire somebody for something like this. Assuming they are a valuable employee I'm just not going to fire them for something as trivial as this. It was a lapse of Internet judgment. She was probably drinking at the time. Drunk people say all sorts of stupid things... and we haven't fully adapted yet to this world where stupid stuff you say in the bar no longer stays in the room but is transmitted around the world in seconds. I would however call them into my office and privately counsel them on how poorly this reflects on them, as well as on the company, and please--- fortheluvvaGod be more careful.