She's not rising to his baiting. She keeps deflecting him, saying things that are damnably reasonable when he wants her to get upset so that maybe he won't feel the nagging sense of owing her anymore. He needs an excuse and she's not giving him one.

Time to go nuclear.

"Then why do you keep on? You're temporary, you know. Even if you don't get yourself killed you'll get old. You'll wither, lose your...charms, and Cooper will move on to greener pastures. You're mortal; that means you're replaceable."