Bert,
If you want to take it to the next step on Facebook, you can report this person for what Facebook calls "abuse". Find your ex-patient's Facebook page. You won't be able to see the actual wall post or much other information, or post a comment, unless this person has "friended" you. However, you can submit an "abuse" report by clicking the "Report/Block this person" link at the bottom of the left column on the abuser's profile. In the window that opens, check "Inappropriate Wall Post". The complaint is anonymous.
That's as far as I'd take it. You could send a message, even to a stranger, by clicking the link "Send (name) a message" under the Profile Picture at the upper left. But that may open a can of worms.
Anyway, don't worry about this ex-patient's friends seeing her defamatory post. John's first rule of social networks: Morons generally have morons for friends.
