Herta being your girlfriend means that she would have little time for you. So because she don't want you to feel lonely she gives you one of her puppet to you hoping that you'll feel less lonely and don't miss her as much

However seeing you give the puppet a little too much affection irritate her. "I'm the real one here, is my puppet really that adorable?" Pang of jealousy fills her heart, how can she be jealous over her own puppet? Especially when she's the one who allow it in the first place?

But she had enough when she sees you cuddling the puppet. She walks over to you and takes the puppet from you

"That's enough!"