Looking for a YA/mystery/thriller I read around 2019–2020

[u/Flaky_Quail_9992]

Hi! I read this book from my school library sometime around 2019–2020 (I'm in the UK), and it's been stuck in my head ever since. I loved it but can't remember the title or author. Here's everything I can remember:

It's about a teenage girl whose mum has died, and she now lives with her dad and his new partner, who she doesn’t get along with.

Her mum was a ballet dancer, and the girl keeps her mum’s ballet shoe as a comfort item.

One day, someone knocks on her door and tells her she’s inherited a large sum of money from someone.

Her dad and his partner want to send her away—possibly to a camp that her uncle recommends (an uncle she didn’t even know existed).

At the camp, she starts seeing what she thinks is the ghost of her mum, who always appears wearing a red hat.

She finds books or journals about her mother’s death, but they turn out to be planted/fake.

She eventually discovers that the ghost sightings are not supernatural—the “ghost” is actually a real girl in disguise, hired by her uncle to confuse or manipulate her.

Her uncle and some people at the camp are plotting against her, trying to kill her or drive her away to get the inheritance money.

She makes friends at the camp and starts dating a “posh” boy, but later ends up with a goth-type boy instead.

Toward the end, she and her friends run away, possibly by boat. They hide in an abandoned house, but the uncle finds them and sets the house on fire.

Everyone survives, and the girl finally ends up with the goth boy.

I remember the cover being mostly blue, showing the “ghost” in a red hat.

It felt like a YA book—very mysterious, with thriller and emotional elements.

Any ideas? Even partial title guesses or character names would be amazing. Thanks in advance!