YA Ghost Girl Story

I'm trying to figure out the title of this book I read several years ago, published in the 2010's. Some of the details below might be incorrect...

It's about this girl who was murdered, and she needs to figure out who killed her in order to move onto the afterworld. For the majority of the book, she's stuck in this in-between world - to her, it's inside a mall. I believe there is a detail in the book about how some ghosts get stuck in this daze and walk aimlessly around the mall, and it's almost impossible to get them out of this daze - near the end of the book, she experiences this as well. She also meets a ghost boy in the book, although I don't think that's a major plot in the story. I want to say that she was killed either before or during a wedding (possibly between her stepmother and her father?)

I also want to say that the cover of the book is of a girl standing/sitting on black stairs?

>1 AlessiaJames: I have to mention Heaven Looks a lot like the Mall even though she isn't murdered. There's also Remember Me though I don't remember enough details to confirm that everything matches your description.

>1 AlessiaJames: This is a guess since I don't remember if the book had a mall theme in it, but perhaps it's Between by Jessica Warman? The cover has her sitting on a black swing floating in a foggy void.

>2 RosetheReader: I second Remember Me by Christopher Pike. The version I had was all 3 books together and was a blue cover- different from the linked page but I think it’s what you’re talking about