What was Mildred's reaction to Montag's collection?

Mildred was horrified when Montag revealed the books he'd hidden.

Mildred backed away as if she were suddenly confronted by a pack of mice that had come up out of the floor. 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.