I could convince myself it could have happened through most of the story, but the last paragraph is just over the top.
"Even though she doesn’t work here any longer, I want to reach out and tell her that quitting without notice because she didn’t get her way isn’t exactly professional. I only want to do this because she was an otherwise great employee, and I don’t want her to derail her career by doing this again and thinking it is okay. She was raised in a few dozen different foster homes and has no living family. She was homeless for a bit after she turned 18 and besides us she doesn’t have anyone in her life that has ever had professional employment. This is the only job she has had. Since she’s never had anyone to teach her professional norms, I want to help her so she doesn’t make the same mistake again. What do you think is the best way for me to do this?"
I'm not familiar with askamanager, but isn't making up letters pretty standard and time-honored for advice columnists?