Charlotte's Friends by Sarah Kennedy

Charlotte Pierce has had a solitary childhood, eked out in large houses with empty people doing empty things; the only person who ever remembered her birthday was Cook.
She has two close friends from her schooldays: Barty, an acclaimed photographer, and Therese, who now runs an animal sanctuary. Blissfully ignorant, the two girls don't know it, but Barty and Therese are the most important people in Charlie's life - and she will do anything to keep them.
Sarah Kennedy's first novel is a compelling psychological chiller that examines the devastating effects of a damaged childhood. A mixure of Highsmith and Rendell, a new style in suspense.