It's overused. Way too overused. Almost every story I see is: HARRY X (name) MALFOY.

If you want to make a good story, you may not want to include it. Now, I know what my friend drowning_in_faith did. Her character, Manda, is living with the Malfoys. It's her closest relative. But her parents can't take care of her. That's the reason she is with the Malfoys and says she's a sister to Draco.
That's good! It really is!

But when you use it to date Harry or cause love triangles... No.

Can I just say how Faith put in detail? She made up a good backstory and a good character.

Also, why do I never see someone as Tonks' sister? Or Bellatrix's daughter? Well, forget the Bellatrix part since:

SEWINA AND JASSMINE ARE HER DAUGHTERS. I mean, it's good Roleplay too!