Now I think we are getting into theories of whether he knows or not. Namor is there to protect his people and maybe he was thinking irrationally. I get why he would want her, who the invaders did mention, dead.
All he thought of, from what he said in his introduction, was about this particular scientist inventing the detector. An invention thought to be impossible to do do. Maybe he also wanted to interrogate her into spilling more information on who else might be involved.