Her knee-jerk reaction is to immediately tell Cade that no, of course he isn't a coward, don't be silly. But that isn't going to help him, and what he needs isn't empty reassurances. So instead, she just turns to look at him, voice soft.

"Why do you think that?"

She tries to recall if he did anything particularly noteworthy during the fight that would be considered cowardly. He was pretty scared, but. Being scared of a horrifying leviathan infested with ungodly corruption isn't cowardly, that's just good sense.