Her wording, both here and re Montague, seems to show some concern; what you quoted is preceded by "Malfoy could really have been hurt." Nonetheless, the speed with with she drops the subject is so fast, it's almost like she was just mentioning a stray thought, not that she actually gives a damn. I think even more in line with what you said is her reaction to knocking out Snape in the Shrieking Shack: "Oh, no, we've attacked a teacher, we're going to be in so much trouble." Never mind that a person appears injured. They attacked a teacher. That isn't done! And they could get in trouble! (Except, of course, that it's them, so obviously they won't.)