There's a story on Quotev about Sirius Black having a daughter and her uncle is Lucius Malfoy because her mother was Lucius's sister. I have been looking for about two weeks and I can't find it. I also forget to say she was raised by Remus Lupin instant of the Malfoy and she never knew Lucius Malfoy was her uncle till Draco told her. Her mother is died. There two stories to it I be live but I can't remember
The question is a bit terse, but the summary of The Blackened Desire (published 10 months ago by author lilly) might be a fit:
She was Slytherin’s top student, guaranteed to be Prefect and Head Girl. She was Sirius Black’s daughter, the niece of Lucius and Narcissa Malfoy, the older cousin of Draco Malfoy, and the lover of Hogwarts’ Redheaded prankster, George Weasley. Life for her sounded perfect, didn’t it? But things weren’t always that way. The story starts with Evelyn Black, as an uptight, higher class, blood supremacist girl and George Weasley, the wild prankster, who didn’t have a care in the world. The two combination seemed quite odd, but still… even after all those times… she still remained his Blackened Desire.
You said that her mother "was" Lucius' sister, so I'm guessing she's dead. In this story, Lucius' sister was murdered - officially, by Sirius Black, but the actual reason is something Evelyn is investigating:
"Alex, I've been thinking. What if Mum was poisoned to death?" I saw him roll his eyes at my theory and immediately pointed to the paper, where I had written down all of the evidence. The library at Malfoy Manor was the only place where we could actually talk without getting eavesdropped on. I'm going to be truthful here, without Alex, this library would be deserted.
"No, I'm serious, hear me out. The Aurors found a teacup next to her lifeless body, and despite everything in the house being demolished, the teacup was still intact. What if it was charmed somehow--"
"Evelyn, you know for a fact Uncle Lucius wouldn't be happy if he knew you were investigating this again," I sighed, slumping a little bit, before straightening up again. My mum was murdered when I was two years old. When, why, and how, still remains a mystery to this day.
Well, to me and my brother, Alex, of course. The ministry, however, thinks my dad, Sirius Black, was responsible for her death and the death of twelve muggles. So, as a result, he's been in Azkaban ever since I could remember.
Eventually found with the Google query
lucius niece "daughter of" sirius black uncle site:quotev.com