Trettel, who started for ASD Cauriol, made her international debut at an FIS race on March 12, 1995 in Kitzbühel . She won the giant slalom ahead of Ursula Fingerlos , before finishing third in the parallel slalom a few hours later. At the end of November 1995 she made her debut in the giant slalom in Zell am See in the Snowboard World Cup , where she finished in the points as fifteenth. A little over a week later, she reached the podium for the first time in Altenmarkt-Zauchensee as third. In January 1996 Trettel started for the first time at the snowboard world championships . She took eighth place in the giant slalom and 14th place in the parallel slalom in Lienz . She finished her first season in the World Cup in 19th place in the overall World Cup ranking.
Since the winter of 1996/97 Trettel has been one of the world's top snowboarders. In the giant slalom in particular, she was one of the best athletes, as evidenced by her first World Cup victory in Lenggries, Germany, in early 2017. Trettel also competed in snowboard cross competitions this season , where her best result was eighth place in the Sun Peaks Resort . At the Snowboard World Championships in San Candido in 1997 , however, she only competed in her parade disciplines giant slalom and parallel slalom, where she reached ranks 9 and 15. She finished ninth in the overall World Cup, while she just missed out on the podium in fourth in the giant slalom special classification. She achieved this after another World Cup victory and podium finishes one season later when she finished the 1997/98 World Cup in third place in the giant slalom classification. At the 1998 Winter Olympics in the Japanese Nagano she finished behind Karine Ruby , Heidi Renoth and Brigitte Koeck fourth place in the giant slalom, which she narrowly missed a medal.
In the winter of 1998/99 Trettel won a World Cup race in parallel slalom for the first time in Tandådalen, Sweden . At the Snowboard World Championships in 1999 in Berchtesgaden , however, she only finished tenth in this discipline, whereas she won the silver medal in the giant slalom behind her teammate Margherita Parini . In December 2000 she won her fifth and final World Cup victory in the parallel giant slalom in Ischgl . However, she celebrated her greatest career success at the 2002 Winter Olympics in Park City , where she was third behind Isabelle Blanc and Karine Ruby and won the bronze medal in the parallel giant slalom. A year later she achieved her next top result with fourth place in the parallel giant slalom at the Snowboard World Championships 2003 in Kreischberg .
In the years that followed, she repeatedly achieved placements among the top ten, but was no longer able to constantly catch up with the world's elite. After the 2005/06 World Cup season , Trettel ended her career.
Italy
World cup
Lenggries
Tandådalen
Naeba
Ischgl
2002 Park City
2005 Whistler