The Vanishing by Wendy Webb

Recently widowed and rendered penniless by her Ponzi-scheming husband, Julia Bishop is eager to start anew. So when a stranger appears on her doorstep with a job offer, she finds herself accepting the mysterious yet unique position: caretaker to his mother, Amaris Sinclair, the famous and rather eccentric horror novelist whom Julia has always admired . . . and who the world believes is dead.

When she arrives at the Sinclairs' enormous estate on Lake Superior, Julia begins to suspect that there may be sinister undercurrents to her "too-good-to-be-true" position. As Julia delves into the reasons of why Amaris chose to abandon her successful writing career and withdraw from the public eye, her search leads to unsettling connections to her own family tree, making her wonder why she really was invited to Havenwood in the first place, and what monstrous secrets are still held prisoner within its walls.