This is the choke point -- she has been trying to avoid Rosinante and Law (Law's easy right now) since the fight, but boarding the submarines gathers everyone tightly together. And she can't exactly deny what's plainly obvious.

So when he speaks to her, she sighs and doesn't bother to prevaricate.

"I was." Does the distinction matter? To her, a great deal. To him? She's not so sure.