Mark of an Angel (2008)

Elsa, a woman with a long history of depression, in the midst of a divorce from her husband of twelve years, develops an obsession with a seven year old girl she sees at a birthday party when she comes to pick up her son Thomas. Determined to find out more about the girl, Elsa uses Thomas as a way into the girl's family, by helping a friendship develop between Thomas and the girl's brother Jeremy, so that in turn Elsa can befriend the girl's mother Claire. She uses Thomas more and more in her pursuit of this obsession, telling her employer and fellow employees that Thomas is seriously ill so that she can run off and watch the girl (Lola) wherever she goes. Elsa even tells her parents lies that she is going out with a friend so they will baby-sit so Elsa can even go as far as hiding in the bushes outside of Lola's house, and watching her at night. At first Claire doesn't suspect anything, but gradually notices that Elsa is paying too much attention to Lola, and confronts Elsa. Elsa in turn claims that she knows that Lola is her long presumed-dead daughter and somehow Claire has stolen her.