首先，資料來源是原版角色對話與wiki資料。
已知資訊有:
1.一開始有嚮往都市、討厭鄉下的傾向(海莉的對話)
2.高中時期在學校很受歡迎(開發者更新介紹)
3.父母過去兩年一直在世界旅行(艾米麗的對話)
4.生活富裕(能有1000多條裙子、100多雙鞋子以及自己搞了一間暗室)
5.與姐姐艾米麗同住在父母的房子裡，但是關係算不上親密(海莉2心事件以及艾米麗的對話等等)
6.喜歡打扮(海莉的對話)

接著是結合背景設定來建立一個基礎。
首先，從第一點來看，海莉有可能在都市生活過一陣子才產生了這種傾向。再配合高中並沒有說明在哪，算是一個模糊空間，因此我設想中是在就學時期就讀位於都市的學校，並且為此在都市生活過一陣子。接著是第三點，父母長期旅行，遊戲中也沒有要回來的傾向，結合第四點生活富裕，這時候我腦海中就有了個想像，父母可能早期忙於事業，而海莉住在城市讀書，之後又是父母長期旅行，造就了對海莉而言父母基乎等於不存在，有的只有源源不斷的錢。

父母缺席加上與姊姊的關係也不算好，這樣一來海莉成長過程中可能會缺乏安全感也沒有情感支持。但因為有充足的錢，配上不差的外表，自然而然就靠著打扮與刻薄的言行來武裝、保護自己，彌補自己的不安全感。一個善於打扮又長得好看的人自然會在學校受歡迎，但是對於海莉而言可能反而會覺得所有人都是被自己外貌吸引來的，並沒有人真正理解自己，進而加深不安全感。哪怕回到鄉下，因為沒有別的能夠彌補不安全感的方式，所以就維持著執著於打扮的行為，這算是無意識中的結果。因為鄉下不方便購物，於是就開始嫌棄起鄉下，懷念起之前的都市生活了，這樣就能解釋前面的第一點。這樣的海莉突然遇到了一個她覺得能夠理解自己，並且能夠依賴的人，自然就變得一發不可收拾對這個人有著過度的依賴，甚至會為了確保自己能夠一直依賴下去而有一定程度的控制欲。

這樣一來病嬌版海莉的設定就基本完成了，會是一個有著嚴重不安全感，對特定對象過度依賴的病嬌。雖然好像有種講歪理的感覺。

將病嬌化的過程分配到好感度裡差不多就是以下這樣:
0心:對一個放棄大公司工作、都市生活的人(也就是玩家)有些好奇，好奇怎麼會有這種決定，但也僅此而已，所以基本上跟原版不會有太大變化。
2心:開始對玩家本人產生興趣。
4~10心:基本上就是依賴情節愈演愈烈，從會主動克制到無法克制。
婚後:因為結婚所以病嬌程度有所緩解，但只要有點契機依舊能爆發的感覺。

不過我的文筆有限，可能讓人覺得這不夠病嬌，或是讓人體會不出設定是這樣子，還請見諒。
(The following uses machine translation.)
First, the sources of information are the original character dialogues and wiki data.
The known information includes:
1.She initially had a tendency to yearn for the city and dislike the countryside (as seen in Haley's dialogue).
2.She was very popular in high school (as per the developer’s updated introduction).
3.Her parents have been traveling the world for the past two years (as seen in Emily's dialogue).
4.She lives in affluence (owning over 1,000 skirts, more than 100 pairs of shoes, and even created her own darkroom).
5.She lives with her sister Emily in their parents' house, but their relationship is not particularly close (as shown in Haley's 2-heart event and Emily’s dialogue, etc.).
6.She enjoys dressing up (as seen in Haley's dialogue).

Next, I will establish a foundation by integrating the background setting.
Firstly, based on the first point, it seems likely that Haley developed this tendency after living in the city for a while. Additionally, since her high school location is not specified, it remains ambiguous. Therefore, I envision her attending a school in the city during her education, having lived there for some time. Moving on to the third point, her parents have been traveling for an extended period, with no indication they plan to return in game. Combining this with the fourth point about her affluent lifestyle, I imagine that her parents, occupied with their careers early on, left Haley in the city to study. Later, as her parents continued their travels, they essentially became absent from her life, leaving Haley with nothing but a constant flow of money.

With the absence of her parents and a strained relationship with her sister, Haley likely grew up feeling a lack of security and emotional support. However, with ample wealth and good looks, she naturally relied on her appearance and sharp words as a means to armor and protect herself, compensating for her insecurities. A person who is skilled at dressing up and possesses beauty would naturally be popular in school, yet for Haley, this might have led her to feel that everyone was merely attracted to her looks, with no one truly understanding her, which only deepened her insecurity. Even when returning to the countryside, with no other means to ease her insecurity, she continues to obsess over her appearance, an unconscious result. The lack of shopping convenience in the countryside leads her to resent it, longing for the city life she once had, thus explaining the first point. When such a Haley encounters someone she feels can understand and depend on her, she becomes overwhelmingly reliant on that person, to the point of developing a desire for control, ensuring she can continue to rely on them.

Thus, the foundation for the yandere version of Haley is essentially complete: she would be a character with severe insecurity, excessively dependent on a specific individual. Though it may seem like a distorted logic.

The process of her transformation into a yandere is reflected in the affection system as follows:
0 hearts: She is curious about a person who gave up a corporate job and city life (the player), wondering what could have led to such a decision, but that’s all. Therefore, there isn’t much change from the original.
2 hearts: She begins to develop an interest in the player.
4-10 hearts: The dependency gradually intensifies, starting with attempts at restraint but ultimately becoming uncontrollable.
After marriage: The yandere tendencies are somewhat eased due to marriage, but they can still erupt with even the slightest trigger.

However, my writing skills are limited, and it may not fully convey the yandere aspects or may not allow others to fully grasp the intended setting. Please forgive me.