Her:
Empty feeling
Doesn't speak, but rarely does
No yandere
Doesn't move much
Says "WHYYYYYY?!" loudly, when she's sad
Used to get angry when someone calls her "Pettan" or someone talking to other girls, but since she lost her anger and possessiveness, she's unable to get angry
Stoic
You're currently not her obsession

In order to make her go yandere Aka. Back to her normal state, Injure and annoy her countless of times, she'll then snap

Your goal:
Make her possessive and a yandere again