Between Two Strangers by Kate White

 Skyler is a struggling artist in NYC and kind of a loner. One day she gets a call from an attorney saying she has been left an inheritance by a man who recently died of pancreatic cancer. Except she doesn't remember ever meeting the guy. Then the lawyer mentions his nickname and Skyler suddenly remembers having a one-night stand with the man 12 years earlier. But why would he leave her millions of dollars when they hadn't been in contact since that night? And why are strange things starting to happen to her--a break-in at her apartment, a mysterious man showing up at her work studio?

This poor girl seems particularly isolated. She has been estranged from her mother since the death, years earlier, of her sister. And she has let most of her friendships fade away since her sister's death. So she feels particularly vulnerable. It's a good suspense story with some interesting twists along the way.