Hmm fear would just encourage him to want to kill her in self-defense if he thinks she's a threat. Lunairan soldiers are trained not to back down in a fight unless they receive orders to do so from a higher up. Also, fear tends to make people more irrational, so he'd be even less willing to talk.

She could pull the a similar trick that Cassie did on Serix by pretending to beg for her life and saying that she'll lead him to other humans if he doesn't kill her. That would work, because he would want the bragging right to say he wiped out the rest of the humans. When they're in the plane, maybe she could trick him or catch him by surprise somehow and cuff him to something in the plane, so he couldn't kill her or tell the other Lunairans where she is. They'd end up at kind of a standoff, because he'd be stuck there against his will, and she wouldn't quite know what to do with him either.