The Big Apple Effect by Christy Goerzen

After a lifetime of New Age "adventures" with her weirdo hippie mom, fifteen-year-old Maddie is realizing a lifelong dream and visiting New York City. Armed with her 130-item to-do list, Maddie hits the streets of New York with her friend Anna and Anna's brother, Thomas. Maddie drags her friends around on an epic quest for the ultimate art-show outfit, oblivious to the fact that they don't share her passion for vintage clothing. Three days into the trip, a most unwelcome surprise—the arrival of Maddie's mother—threatens to derail the entire adventure. As her mother's obsession with dietary trends and fortune-tellers takes center stage, and everyone's tempers get thin, Maddie has to face some ugly facts about how she's been treating her friends.