Evelyn was born in a pureblood household, daughter of Seth Alfred McCarthy, a very prominent and powerful Ministry figure. Her mother was his wife, an unnamed Veela woman whom passed away during childbirth. She is left unnamed because Seth never told Evelyn anything about her, and instructed his house elves to do the same out of a sick, sadistic sense of revenge.
She was blamed for her mother's passing by a mentally unstable father, and lived as the remembrance of what she had taken away ever since - and certainly was treated in such a manner. As she got into elementary school age, that sadism morphed into the occasional employment of the Cruciatus curse. In moderation, of course - wouldn't want the girl to get too damaged to continue this little game.
The house elves were sworn to secrecy, and Evelyn grew too scared of her father - if she didn't tell anyone, perhaps she wouldn't set him off even more. She was a very quiet child, keeping to herself and her books, studying magic on her own. As the sadistic behaviors escalated, her father decided to move to a slightly more isolated town - Narrie - so he could continue his deeds unpunished. This, however, provided her with the opportunity to attend the local dojo. Her father had the presence of mind of making it seem like Evelyn had a normal life, and knew she had to look the part - he didn't think too much about enrolling her once she requested it.
Her activities in Hapkido and Krav Maga, as well as the friendliness of people she met at school as a Sturt, both combined to make her feel more confident about herself slowly over time. As the years went by, she started showing that confidence more and more - she grew an excellent sense of humor, made many friends, became flirty, took excellent care of her looks and wear, and near the end of her academic life she seemed very far removed from what a Sturt should embody.
Of course, this also meant she came to resemble her mother too much. At home, things got worse - her father started to beat her up physically rather than just settling for watching her squirm, needing to take out the violent anger bubbling inside from watching the woman that took the love of his life away also take away her looks and personality. It all came to a head when one time, near the end of her last school year, she accidentally killed Seth in self defense.
At first, she was shocked - not that he died, but that she killed someone. But then, she realized she didn't feel particularly bad about it, such was the hatred she harbored for the man. Able to keep her cool due to lack of attachment, she eventually came to a conclusion: if she was to come out and claim her father abused her, her name would be devalued and she would be looked at with pity for the rest of her life. If she made it look like a robbery, she could turn it into a redemption story that kept the name strong going forward.
And so she did. Shedding away as much evidence as she could, she made sure to change the elves' memories before she reported the incident. When questioned, she employed her incredible Occlumens skill as her defense. It all went very smoothly and the people whom knew her rallied behind her, wanting her to succeed. It was her first taste of manipulation, and she rather liked it.
It was all downhill from there as she descended further and further into these mannerisms and behaviors as time went by. Her excellence in magic made it so she was actually a candidate for Auror training, which she aced - she became a full-fledged Auror as soon as she was able, and made sure her competence was always on display just so to allow herself an easier climb up the career ladder later down the line. She arranged her marriage to someone whom had the same intentions, and whom also had reasons to keep themselves hidden. She became a close friends to her husband in reality, and a very loving couple to everyone else. They don't love each other, and they're perfectly okay with the fact.
The only speck of hope in her life came in the form of her adopted daughter, just a few years after the life changing incident. While traveling to a location that was protected from Apparating, Evelyn had gotten lost and wound up in a small town in which a tween was being chased to death due to fear, due to being magical. Her parents had died and her powers had revealed themselves on accident very publicly. Evelyn decided to take her in so to save her, out of an unknown urge; she has grown to care for the girl very deeply ever since, even willing to give up her power so to ensure this girl is alright. Perhaps this is a sign of Evelyn not being too far gone.