YA fiction (I read in 2022, though it was probably publish in the 2010) - girl is sent to boarding school in Europe following her best friends death

[Elizabeth]

Girls name starts with a C I think maybe Cearra?
Her best friend died in a car crash and she constantly calls her friends cellphone just to hear her voice on the voicemail.
The girl was in a secret relationship with her best friends boyfriend (when her best friend found them at a party together she drove off and ended up dying in a car crash).
She was between 15-19 years old.

[Becca]

The Year After You by Nina de Pass?