I've never cared that much for Irma Pince, but you gave her edges and depth in this story that make her appealling and interesting. Starting with this wonderful line that seems to capture her personality:
Looks alone were for the sorts of people who weren't interested in depth or meaning, and were a lazy way to judge anything, weren't they?
This line came back to me again and again as I read, becoming especially compelling when Tom Riddle moved in and out of the story.