Ummm, well, if I'm to guess, then my guess is Lucious Malfoy. Draco was very upset with her not agreeing with him about the HippoGriff, to get killed, and Hagrid to get fired. He has made it obvious that he keeps his dad apprised on the goings on at Hogwarts. Then, the way you wrote,
Quote:
“Let.Go.Of.Me.” Emily struggled against the firm grip, but to no avail.
leads me to believe that it is an adult that has ahold of her, so firmly, that she can't get away. And Lucious is the only adult that she would talk to that way. I think Lucious malfoy went to the school to be the continued, thorn in Dumbledore's side, and to threaten Emily into submission. Just my guess. I'm sure whoever it is, it'll be great the way you write it.