She has been warned often, and knows the rule.

I kept her after school because she broke that rule, and if she breaks it again, she will be punished again.
I kept the Edwards boy two hours yesterday and--" "Edwards boy! Do you mean to compare that--that young rip of a Ben Edwards with a girl like Bos'n?
I never heard--" "I'm not comparing anybody.

I'm trying to be fair to every scholar in this room.

And, so long as Emily behaves herself, she shall be treated accordingly.

When she doesn't, she shall be punished.