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Le Sommer began playing football at the age of five joining the women's section of Trélissac FC. After a four-year stint at the club, she joined AS Guermeur in the Brittany region. She later played at one of the biggest clubs in the region, FC Lorient, and earned many honors in the youth section of the club helping her youth sides win the Coupe Fédérale 16 ans in 2005 and the Mozaïc Foot Challenge in 2006, with the latter being held at the prestigious Clairefontaine academy. Le Sommer was later selected to attend CNFE Clairefontaine, the women's section of the Clairefontaine academy. After a short stint there, she joined D1 Féminine club Stade Briochin. In her debut season with Briochin, Le Sommer appeared in all 22 league matches scoring four goals. The 2008–09 season saw her score 10 goals in 22 matches. For her efforts, she was nominated for the UNFP Female Player of the Year losing out to Lyon player Louisa Necib. Le Sommer got off to a fast start for the 2009–10 season scoring ten goals in her first seven league matches, which included a hat trick against Toulouse in a 4–5 defeat. She finished the season as the league's top scorer and was awarded the UNFP Female Player of the Year following the season.
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