Little universes / Heather Demetrios.

Enhanced descriptions from Syndetics:

Heather Demetrios's Little Universes is a book about the powerful bond between sisters, the kinds of love that never die, and the journey we all must make through the baffling cruelty and unexpected beauty of human life in an incomprehensible universe.

One wave: that's all it takes for the rest of Mae and Hannah Winters' lives to change.

When a tsunami strikes the island where their parents are vacationing, it soon becomes clear that their mom and dad are never coming home. Forced to move to Boston from sunny California for the rest of their senior year, each girl struggles with secrets their parents' death has brought to light, and with their uncertainty about the future. Instead of bringing them closer, it feels like the wave has torn the sisters apart.

Hannah is a secret poet who wants to be seen, but only knows how to hide. The pain pills she stole from her dead father hurl her onto the shores of an addiction she can't shake and a dealer who turns her heart upside down. When it's clear Hannah's drowning, Mae, a budding astronaut suddenly launched into an existential crisis--and unexpected love--must choose between herself and the only family she has left.