How does Mildred react when she finds out what’s in the ventilator?

From the text:

He could hear her breathing rapidly and her face was paled out and her eyes were fastened wide. She said his name over, twice, three times.

Then moaning, she ran forward, seized a book and ran toward the kitchen incinerator.

He caught her, shrieking. He held her and she tried to fight away from him, scratching.

"No, Millie, no! Wait! Stop it, will you? You don't know . . . stop it!"

He slapped her face, he grabbed her again and shook her. She said his name and began to cry.