I would hope it's supposed to be anonymous to Facebook - after all, there were some fairly frank discussions on topics that aren't exactly public knowledge (e.g., Facebook tracking clicks and other little bits of things that really should be revealed by PR, not an employee in an unsanctioned conversation).

"Who's to say 'she' isn't a composite or fabricated anyway?"

Well, in that case the author never visited Facebook's offices - that's the detail that gives away the employee's identity. Given the level of detail gone into by the author, I doubt this is fabricated.

It would probably be better for everyone if it were, though, because he just made a real big boo-boo that will probably cost someone their job.