Originally from Minnetonka, Minnesota, at the age of 16, she relocated to Colorado Springs, Colorado to train with noted coach Carlo Fassi. Trenary won the U.S. junior title in 1985. During a warm-up in 1985, she collided with another skater, whose blade sliced Trenary's calf muscles and severed an artery in her left leg.
Trenary placed 5th in her first senior national championships in 1986. Later that summer she won the U.S. Olympic Festival. In fall 1986 she placed second to Elizabeth Manley at the St. Ivel International. At the U.S. championships in 1987, she finished second in both the compulsory figures and short program, where she landed a triple flip jump for the first time in her combination. In the long program Trenary landed four clean triple jumps, including the triple flip, and she upset reigning world champion Debi Thomas to take her first senior national title. At the 1987 World Championships, she rallied from 11th in the compulsory figures to place fourth in the short program, again landing the triple flip jump in combination, and fifth in the long program, to place 7th overall. In 1988, Thomas regained the U.S. title, with Trenary finishing second. Trenary placed 4th at the 1988 Winter Olympics. She was 5th at the 1988 World Championships, where she fell on the triple flip in both her short and long programs. Due to her strength in compulsory figures, Trenary again won the U.S. Championships in 1989, although she was defeated by Kristi Yamaguchi in the free skating. Trenary won bronze at the 1989 World Championships.
In 1990, Trenary won both the U.S. and World titles. Her strength in the compulsory figures was the deciding factor at the 1990 World Championships. She was 5th in the short program and second in the free skate to Midori Ito but her top placement in the figures kept her in the lead overall. The International Skating Union eliminated figures after that season. After she won her World title, her coach, Carlo Fassi, returned to live in his home country, Italy, and Trenary began working with Kathy Casey.
Trenary's triple jumps included the toe loop, salchow, and flip, which was quite competitive for a female singles skater in the mid-to-late 1980s. One of her signature moves was a combination of a one-foot axel into a triple salchow.
In January 1991, Trenary underwent surgery to drain her ankle after she developed a staph infection. As a result, she withdrew from the 1991 U.S. Championships. In March 1991, Trenary moved to Cleveland, Ohio, to work with Carol Heiss Jenkins.