Beneath Blackwood by Courtney N Johnson:
 
After her mother's death, seventeen-year-old Willow Lane is left with questions no one in Blackwood Grove wants answered. The town insists the past should stay buried-but a coded note hidden among her mother's belongings says otherwise.

Each message Willow deciphers leads her deeper into the town's carefully maintained traditions, where faith and power are intertwined and silence is rewarded. As she begins to see Blackwood for what it truly is, the people around her grow watchful-and dangerous.

Uncovering the truth could cost Willow everything. But staying silent may cost her even more.