Then she ought to have put the Ultimate Imposter on the task of going undercover, or at least had them train you.

[She obviously didn't do one, and he's got a very strong impression that she didn't do the other, either.]

So, what enemy was so fearsome that they could possibly be worth putting you on the operation instead? And in that situation, why kill you to prevent your cover from being blown instead of letting you fight? Why bother to put a combatant like you on the task if she was only going to kill you if you slipped up on your acting performance?

There's really only one thing I can think of that would make that decision make any sense.