Kosinski was born in Willingboro Township, New Jersey, and grew up in nearby Cinnaminson Township, New Jersey. She is one of four children of Jeanette, a chemist, and Robert, a retired biologist who worked for the New Jersey Department of Environmental Protection.
Kosinski's early life took place in Willingboro Township, New Jersey, and Cinnaminson Township, New Jersey, where she was one of four children raised by her parents Jeanette, a chemist, and Robert, a retired biologist who worked for the New Jersey Department of Environmental Protection.