Fanchini's first races in the World Cup were the two descents from Santa Caterina on January 6th and 7th, 2005, where she finished 17th on both occasions. A month later she took part in the 2005 World Cup, also in Santa Caterina. In the combination she only reached 20th place (out of 21 rated runners), but two days later the then 19-year-old achieved her greatest success so far: behind Croatian Janica Kostelić and ahead of Austrian Renate Götschl , she won the silver medal on the descent - after falling in training. At the end of February, she also took part in the Junior World Championships in Bardonecchia and won the silver medal in the downhill and the bronze medal in the Super-G.
Fanchini was able to maintain her good form at the beginning of next winter: In the 2005/06 season she won her first World Cup victory in the first downhill race on December 2nd in Lake Louise . After that, however, their results deteriorated significantly. At the 2006 Olympic Games in Turin , she came only on the 29th downhill rank. At the end of the season she reached a ninth place again in the downhill from Åre . In the 2006/07 season , Fanchini reached seventh place in the second downhill run from Lake Louise on December 2nd, but did not get past 25th in all other races. At the 2007 World Championships in Åre, she could not repeat her success from the last World Cup and only finished 27th in the downhill and 31st in the Super-G. In the 2007/08 World Cup season there were only two placements among the top 15.
At the end of October 2008 Fanchini sustained a serious injury in his left knee while training on the Hintertux Glacier and had to take a break for the entire following season. During the 2009/10 season she was among the top 15 in four World Cup races and achieved her first top 10 result in more than three years with tenth place in the Super-G in St. Moritz . At the 2010 Winter Olympics in Vancouver , she reached 14th place in the Super-G. In the 2010/11 World Cup season , Fanchini finished in the top ten in three downhill runs and two Super-Gs, making her a big step forward in the Downhill World Cup in particular and equaling her best overall result from the 2005/06 season with twelfth place. At the 2011 World Championships in Garmisch-Partenkirchen , she was 16th in the downhill and 18th in the Super-G.
In the 2011/12 World Cup season Fanchini achieved four top 10 results. In mid-March 2012 she celebrated the only European Cup victory of her career at a Super-G in Pila . Although she was only placed in the top ten once in the 2012/13 World Cup , she took part in the 2013 World Championships in Schladming , where she finished 9th in the downhill. She achieved a significant increase at the beginning of the 2013/14 World Cup : She finished third in both Beaver Creek and Lake Louise. This successful streak broke off after a short time and she had to accept several failures in a row. At the 2014 Winter Olympics in Sochi , she did not get beyond 14th place in the downhill. Shortly after the end of the season, she contracted a collateral ligament on her right knee and had to take a break from training for several weeks.
In the winter of 2014/15 Fanchini had the most successful World Cup season of her career, when she was among the top ten five times. On January 16, 2015, on the downhill run from Cortina d'Ampezzo , she surprisingly celebrated her second World Cup victory , ahead of Larisa Yurkiw and Viktoria Rebensburg . On the other hand, the 2015 World Cup was disappointing , when she did not get beyond 16th place in the combination. In the winter of 2015/16 she was twice in the top ten, in the winter of 2016/17 only once. Fanchini finished fourth in the first World Cup downhill run in winter 2017/18 . In mid-January 2018, she had to end the season after she was diagnosed with a benign tumor disease . As a result, she missed her fourth Olympic participation. Barely recovered, she suffered another setback in November 2018 after breaking her fibula during training.
On April 22, 2020, she and her sister Nadia announced their retirement from competitive sports.