The Lake House by Sarah Beth Durst

Claire’s grown up triple-checking locks. Counting her steps. Second-guessing every decision. It’s just how she’s wired—her worst-case scenarios never actually come true.
Until she arrives at an off-the-grid summer camp to find a blackened, burned husk instead of a lodge—and no survivors, except her and two other late arrivals: Reyva and Mariana.
When the three girls find a dead body in the woods, they realize none of this is an accident. Someone, something, is hunting them. Something that hides in the shadows.
Something that refuses to let them leave.