@8roku
That confused me too tbh. Thinking it over and rereading it, I think I may have been interpreting it wrong after all.
Now I think that she was actually upset because the principal unintentionally put up a wall between the school and her with his words. He thanks her for saving "their" student--their's, excluding her. If they had said "good job", then that would be including her into the school and acknowledging that she is a part of them and their duty to protect "their" kids. So I think she feels that she hasn't been completely accepted as a part of the school's staff yet.
This line can be interpreted in a few ways so it's kind of confusing, but I think I got it right this time. 😅