When Stewart was 10, she worked as the occasional babysitter for the children of Mickey Mantle, Yogi Berra, and Gil McDougald, all players for the New York Yankees. Mickey and Merlyn Mantle had four sons, for whom Stewart watched and organized birthday parties. She also began modeling. At 15, Stewart was featured in a television commercial for Unilever. She went on to appear in television commercials and in magazines, including one of Tareyton's "Smokers would rather fight than switch!" cigarette advertisements. During her college years, she supplemented her scholarship money through "modeling jobs at $50/hour — which was a lot of money at that time". Her clients included Chanel.