Here's why:
* No confirmed projects: While there have been rumors and speculation about future Harry Potter projects, there is no officially announced project that would involve Fleur Delacour's family.
* Fleur's family in the books: The Harry Potter books only mention Fleur's immediate family – her mother, sister, and brother-in-law. There is no mention of any other sisters.
* Fictional characters: It's important to remember that Fleur Delacour and her family are fictional characters. While fans might create their own ideas, it's unlikely that there would be a new character introduced in a future project without Rowling's involvement.
It's best to rely on official sources for information about future Harry Potter projects.