Terezi hears none of the underlying reasons, but in Shepard's words, she does hear the confidence. That's enough for her. Wherever the Commander ends up, she's certain that she'll be okay; and that is as much as Terezi can ask for. She doesn't have time to ask for anything else.

This is the place where Terezi would want to wish Shepard good luck, but they're both aware that in their line of work, luck doesn't really matter. Skill and determination were more important, and Shepard has that in spades. So Terezi offers a salute instead, lifting her chin and trying to keep her emotions in check.

"Knock 'em dead, Commander. I'll hold down the fort here."