Ertl started skiing at the age of two and a half. At the age of 18 she took part at the Junior World Championship in Hemsedal (Norway) winning a silver medal in Giant Slalom and a bronze medal in Combined.
This was the starting point of a long career. Until 2006 she took part in 430 World Cup races winning 14 of them. Ertl won the Giant Slalom World Cup in 1996 and 1998. She won three Olympic medals and four medals at World Championships (Bronze in Giant Slalom at Morioka 1993, Bronze medalist in Giant Slalom at Sierra Nevada 1996, Gold in Combined at St. Anton 2001, Gold in Nation Team Event at Bormio 2005).
She represented Germany at five Winter Olympics between 1992 and 2006, winning silver medals in the giant slalom in 1994 and the combined event in 1998 and a bronze medal in the combined event in 2002.