SOLVED. YA Contemporary Fantasy novel about an Orphanage, a Game, and a Golden Apple. [s]

[Anna]

Hey! I'm looking for the name of a novel that would have come out around 2010. The main character is a girl sent to an orphanage or foster home where she discovers that all the children participate in this game where they hunt for a golden apple. They play this game by going through some door into an alternate dimension/fantasy world where they can see, do, and experience all kinds of things they can't do in the real world. I remember an older woman who is the caretaker.
Two scenes stand out. When the main character first goes into the other world, she sees the annoying kid as a comet, but she comments that he's wrong because his tail is behind him instead of in front. That scene gets mirrored at the end when she learns to become a comet and appears in the correct tail orientation.
I also remember in the introduction of the book it said the author had a long and fulfilling career as a writer and had died soon after or before publication. This makes me worry that the book may have been published earlier than 2010.
I'd appreciate your help if you have any hints. I've searched for this off and on for a few years and haven't been able to find it. I believe the cover was dark and gold and featured the apple in some way.

[Rainbowheart]

Anything on the Orphanages list?

[Sue]

Not an orphanage, as she lives with relatives; but this sounds like The Game by Diana Wynne Jones (Not to be confused with the book of the same name by Monica Hughes) https://www.fantasticfiction.com/j/di...
It was published in 2008, and she died in 2011.

[Sarah]

I agree with Sue; this has to be Diana Wynne Jones's book The Game. I remember the scene with the wrong tail as well.

The main character is referred to as an orphan in the beginning of the book, and goes to stay with other family members.

Here's the bit with the comet:
"She was taken completely by surprise when a comet came fizzing past her face, with its tail roaring out behind like a rocket. “I’m telling, I’m telling!” it shouted in Tollie’s voice. And Hayley went sideways with the shock of it. She had to save herself by clutching the sharp, icy edge of the strand.

Troy hauled her upright. “Oh, go away and play your own game!” he shouted after the comet. “Are you OK, Hayley?”

“Perfectly, thanks.” Hayley stood up, shaking her icy hand, and stared scornfully after the comet as it roared away. Grandad had told her about comets. “He’s got it all wrong,” she said. “Comets go tail first. Not like rockets.”"

[Anna]

Thank you all for helping solve this! I was a kid when I read this book and I now love Diana Wynne Jones's work so it makes me so happy that the book was one of hers!