The Master sits in front of her, and smiles. Smiles, as if they are going to have a pleasant conversation over supper. But instead he asks her to open her mind, to help him succeed in his plan. And as much as she inwardly fights him, as much as she tries to shut out her mind against him, she can't. So she does as he says.
She can feel all of her energy, everything she is, being ripped out of her. After all of her adventures, after surviving a gunshot to the chest, this is how she's going to die. She knows it. And yet, that's not what scares her. No, she's more worried about the people she's leaving behind, the mess they'll find themselves in. The possibility of them dying.