It was supposed to be. I haven't seen anything like "ghouls" in the high school, and the kekkai should have prevented any of those creatures outside from getting in. Even if it fell, then Kantarou would be the first one to know.

[...] I wouldn't be able to tell you if it is really her fault or not. But if she does try to hurt anyone else, then I'll have no choice but to stop her.

One way or another.