Severance was born in Houston, Texas, the daughter of Martha and John C. Severance. Her father was an IBM Systems Manager who had to move frequently around the world. According to Severance, “by the time I was 11, we’d lived in 12 different places.” Severance and her family also lived in Libya, but in 1967 had to flee the country because of the Six-Day War. The family left the Middle East to return to the United States, and settled in Houston, Texas.
Severance attended Westbury High School and, at age 15, started modeling to make money for college. Although she hoped to become a veterinarian, she could not afford the cost of tuition. After appearing in the “Miss Houston” beauty contest, she was discovered by Alan Martin, a local photographer in Houston who introduced her to John Casablancas. Casablancas signed her up with the Elite modeling agency and sent her on assignment to Paris. During this time she met her future husband, model Eric Milan.