The Immeasurable Depth of You, by Maria Ingrande Mora

Brynn obsesses about death and suffers from panic attacks.  When her Mom catches wind of a post that Brynn posted that reads like a suicide note, her mother freaks out.  Her phone is taken away and Brynn finds herself shipped down to Florida to spend the summer --without her phone or Internet -- with her Dad on a houseboat.  Cut off from her friends, Brynn explores the bayou around her Dad's boat and meets a friendly girl that she's attracted to named Skylar.  But when she tries to tell her father about Skylar, he gets upset:  Skylar committed suicide five years ago.

When Brynn later confronts Skylar, this ghost girl tells another story altogether:  yes, she's dead, but she was murdered.  Skylar can't recall any of the circumstances of her death, but Brynn finally has a strong sense of purpose.  She swears that she'll get to the bottom of it and get justice on Skylar's behalf.  That passion for the cause helps Brynn overcome many of her fears, but exposes buried pain and upsets both Brynn's parents and the bereft parents of Skylar.

A surprisingly poignant story about grief with a slight supernatural note to it.  Those latter elements never become distracting and the focus of the story remains firmly on Brynn taking on responsibility for her healing.  All of the characters are strong, but I particularly liked the adults, who are both respectful and respected (although Brynn has a terrible habit of sneaking off and breaking promises).  I'm somewhat less taken by the busy storyline which features several instances of peril largely unrelated to the story and thus grows distracting.  However, the story delivers a strong pay off in the end that makes this fast read very rewarding.