"Good night, tree."

I've taken major inspirations from Eliza and Angelica's dynamics from the hamilton musical + Hatice and Şah Sultan's dynamic from magnificent century -> both of these dynamics are between a younger and an older sister where the youngest sister falls for the same man that the older sister was yearning for Adalet's parents, Feyza and Yusuf, both died during duty when she was officially adopted into her aunt's family as her step-daughter. 

Adalet's aunt, Meral, was already married to another man when Adalet was brought to their household. Meral was a bit older than Yusuf when they first met, and when he met Meral, Meral knew there would be no future between her and Yusuf. She didn’t have the heart to tell her younger sister about her romantic interest towards Yusuf, as she had seen Feyza’s fragile mental state and suicidal tendencies enough to let these two get closer instead.

Meral's husband had no issue with Adalet's presence in his house, though he would later ask her not to call her "dad" and just call him uncle instead. When I think about it, neither Meral or her husband were hostile towards Adalet BUT that's where Meral's bitterness towards Feyza started to become a problem. Meral herself would not have the heart to just leave her niece into the hands of Schola Progenium, HOWEVER she couldn't bring herself to see Adalet as a part of her family. in her eyes, she was taking care of Adalet out of obligation. This cloud of familial obligation started feeling more like she was taking care of an injured stray animal rather than her own kin, as she would see Adalet as a relief to her own conscience. Thus this is why she wanted to make Adalet depart from the house as soon as possible without outright telling her to leave.

When Adalet herself was old enough to leave (and not return), the night before her departure, Meral talked with adalet one-to-one. emphasizing how Adalet was not a bad kid by any metric, it's just that she couldn’t bring herself to see Adalet as anything but a moral responsibility to take care of. Meral brings the letter that she found back when Feyza started bonding with Yusuf, which was smth written by Feyza to Yusuf but just didnt see the light of day due to a typo that made her write a new one while keeping this faulty one as well.

She explains to Adalet why she could never find the urge within her to see her like her own kid when her deceased sister used to be so head-over-heels about Yusuf, and how as the older sister, she had to suck it up and not ruin Feyza's relationship with both Yusuf and each other. Sometime after her triumph (where she had a huge victory streak as an Astra Militarum Commander and became a serious target for the heretics) she's abducted and was subjected to interrogational torture, and when her abductors grew tired of her unwillingness to collaborate with them, they just...forcefully open her mouth, get a hold of her lower jaw and just. rip it by hand and when the jawbone was disconnected from her skull, they used a blade to cut off the jaw and the skin on it completely and as they're tending to the scar that was left after this, Adalet, naturally, becomes feverish and starts disassociating from her current situation oh how pitiful it was for her to beg for her aunt/stepmom. She knew she wasnt wanted in her presence, but at that moment? she hoped her battered state would make Meral pity her. She waited for her aunt and uncle-in-law to come visit her while she's recovering in the military's infirmary, only to be told how she's no longer a child and that she should expect incidents like this since she's in the Astra Militarum now.

Through the events of Rogue Trader, Adalet lies to Heinrix about her relationship with her aunt as she described Meral as someone both physically and verbally abusive BUT after this letter she feels so bad about lying about her abuse, in which she confesses that she had made up some stuff to make her aunt look bad in his eyes. She tells him that otherwise this subtle exclusion by her own family shouldn't have hurt this much, “people have gone through much worse stuff, kids her age at that time had to face worse types of isolation in the military orphanages!” So in return, Adalet thinks people might see her as weak for feeling hurt about something that many would be grateful for .