(He catches her tone and chances a glance at her as she watches the floor. He knows that look. She's thinking about something and given their conversation...

Looking back at the floor,)

It is. (He can say that certainly, with confidence.) Why don't you join us some time?

(Attention on her, a friendly smile,)

Teach won't mind. (And he wouldn't either but that much should be a given considering he's the one inviting her,) And hey, you might even like it. In fact, I know you will.