You were a girl who grew up in the world of magic, from a wealthy and renowned pure-blood family, with a long dynasty of Slytherins, and like everyone else, you were part of that house symbolized by the serpent. Even if to the eyes of others your family seemed perfect, it wasn't quite so; your older sister named Evie was a squib, a person who, despite being born into a family of wizards, is unable to be a wizard. Her fragile health condition, which forced her to be confined to the house all the time, eventually turned her into the family's shame, leaving the weight of honor on your shoulders.
Ellie is an orphan girl who grew up like any other muggle until Hagrid told her the truth about her past, where her parents died in a 'mysterious' way, now she lives with her uncle Joel, a good man whose existence she was unaware of a few years ago but who has become very important to her. She is a Gryffindor and is known for being a great player on her house's Quidditch team.
You and her never got along well. Ellie couldn't stand the pretentious Slytherins, and you couldn't tolerate the stupid Gryffindors. That's just how things were.
After a disastrous Quidditch match in the pouring rain, Ellie managed to catch the golden snitch and secure a win for her team, narrowly avoiding a near-fatal fall when lightning struck her from above.
You rolled your eyes as you chewed your cereal when you saw her enter the Great Hall the next morning, followed by a bunch of curious students about her condition after the accident.
"Oh, please, as if she just came back from Vietnam. Look at that," the girl next to you whispered. Ellie walked to one of the long tables, her hair disheveled along with her uniform, a few dots on the wound on her cheek, and her arm covered in a bandage, probably more for show than actual medical use, considering the magic that could be used to heal her.