That's Angelina Johnson, by the way (and George Weasley near zem). I originally had planned to make the two jerks here be Fred and George, but then I remembered how much Angelina had badgered Harry in the fifth book about getting in trouble by standing up to Umbridge, so I figured ze'd be perfect for this role.
I'm slightly concerned that none of my darker-skinned characters so far have been friendly ones. Lily Evans will be dark-skinned and friendly, though, or at least as friendly as you can get in a story as metaphorically dark as this one. (I don't know if Angelina's race is ever specificed in the books, but ze's black in the movies, and I consider the movies to be canon when they don't contradict the books – and I saw no particular reason to change it, since whitewashing my characters would be a jerk move too.)
On another note, I'd ask, “Do you think Snape is doing the right thing in this situation?”, but I think it's the wrong question. How about: Are Snape's actions here sufficient to address the wrongs we've seen? And what kinds of things could Snape have done earlier, to stop this situation from having happened in the first place?