The Opportunist by Elyse Friedman

When Alana's brothers, Martin and Teddy, contact her and ask her to help them get rid of their father's much younger girlfriend, Kelly, she ignores their calls. Alana is perfectly happy living with her daughter, Lily, and not having anything to do with her wealthy family. But when Martin offers her $50,000 to approach Kelly and offer her money to leave for good, Alana agrees. Soon, Alana finds herself entwined again with her family, and it's hard to know who to trust--especially with so much money at stake. A great read-alike for Peter Swanson.