The closest I have read to that lately was The Face on the Milk Carton, by Caroline B. Cooney. It was good, but I'm not sure it's what you're looking for; it is about a girl finding out she was adopted, and her parents finding out that their bio-daughter, who'd left them this child to adopt, hadn't actually been the mother: this was a stolen child. It does result in the protagonist re-embracing her adoptive parents, who love her and whom she loves, while reaching out to meet the family who raised her for her first three years.

If I find anything more suitable, are you still looking?