[grkvlt]

The most likely explanation is they sent her a message saying pseudonyms are not allowed, and asking for her real name. She replies something like 'My real name is XYZ, here is ID to prove I am a real person, but I do NOT wish to use that name, please continue to call me ABC on the site' but Facebook simply went ahead and changed her name from ABC to XYZ against her wishes. No secret data mining, information collection or machine learning required.