User blog comment:DiegoAnime3000/Just wanted to point this out./@comment-96.254.157.84-20140801063026/@comment-11188061-20140801065111

Some should recognize her, and even remember the past Cinder.

She likely has shed her old personality, looks and appearances completely for a new one. Thus why she's confident enough to infiltrate Beacon. In the Afterbuzz, when asked the relationship between Cinder and Ozpin, Monty mentions that being a headmaster means having a past with a lot of students.