Bell was born in New York City, the daughter of Robin Bell, owner of the design firm www.robinbelldesign.com in New York City, and Harvey Siegel. Her father is Jewish and her mother is a W.A.S.P.. She has an older brother named Luke Bell Siegel who owns a sliding wall and door company called Raydoor in New York City. She also has two half-sisters, Courtney and Mackenzie.

Bell attended Westminster School, Connecticut in Simsbury, Connecticut and then attended Skidmore College in Saratoga Springs, New York before transferring to Rose Bruford College in London, England. There, she landed roles in several theatrical productions, including The Seagull and The Pentecost. She remained in London for a year after graduating, then relocated to Los Angeles, California.