Anya's Ghost by Vera Brosgol

Anya's Ghost - 

Vera Brosgol
Anya Borzakovskaya emigrated from Russia to the EUA with her mother and little brother. Besides the usual difficulties with fitting in high school she has the added memories of being bullied for being an immigrant - she worked hard to lose her native accent, to fit in and not to be considered "fresh off the boat". It doesn't help that her mother insists she should be friends with Dima a nerdy teacher's pet who keeps getting beat up.
Anya has a hopeless crush on Sean, the school's star basketball player, who is in a relationship with her classmate Elizabeth, the perfect teenage girl.
After an argument with her best friend Siobhan crowning a dreadful day, Anya goes for a walk... and ends up falling down a disused well. As it turns out, the well is already occupied by a skeleton... and its respective ghost, Emily.
After being rescued, Emily accompanies Anya and helps her out: she reads fashion magazines and starts choosing Anya's outfits, she floats around the classroom reading the other student's answers and whispers them back to Anya, she stalks Sean and does everything to make Anya cross his path.
Emily lost the love of her life during WWI, and was murdered along with her family shortly afterwards, so she decides to vicariously live the life she didn't get through Anya - which includes getting Anya together with the boy of her dreams.
But is Sean really the boy Anya thought he was? Does she even love him?
And Emily... is she really who she says she is?
In this book we learn that no one is exactly as they seem, there is always more to them than meets the eye, and that being true to yourself is more important than the fleeting popularity of high school.
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