Shine, Coconut Moon by Neesha Meminger

Brown-skinned Sam is 17 and lives in New Jersey with her mom. She has never seen a picture of her father and has no idea what her grandparents are like, except for what her mother has told her, which is basically that they made her life hell and she doesn't want Sam to have anything to do with them either. A few days after September 11, 2001, a man in a turban rings their doorbell. Sam discovers that this is her mother's brother, Sandeep. He is a wonderful man. Sam is about to undergo a crash course in Sikh culture and face the realities of racism head-on as she comes to terms with her true identity.