Shen Nan was touched and disgusted by Chen Mu's insight into the cowardice in her heart. She hated him for exposing her nakedly and examining her without caring whether she wanted to or not. She also didn't understand why Chen Mu was so keen to explore her, at least in her feelings, making her go back and forth between yes and no.
Purpose: Most of us are sincere, but we are afraid to reveal ourselves because of our suspicion of others' sincerity.