"She would refuse anyway. She was frightened when she shot at me on Takodana." Possibly because he was still a faceless monster who didn't so much as slow down in spite of her best efforts to stop him. The kidnapping that happened after that likely didn't sweeten the memory.

He's not invincible, but Chewbacca and Kitty owe some of their success to his emotional distress and the element of surprise. Taking him down should have been more difficult.