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 Brittanyregion. 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 Saint-Brieuc, 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 Olympique 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.
Le Sommer has been active with the women's section of the national team. She has earned caps with the women's under-17, under-19, and under-20 teams. With the under-19 team, she participated in both the 2007 and 2008 editions of the La Manga Cup, as well as both the 2007 UEFA Women's Under-19 Championship, as an underage player, and 2008 UEFA Women's Under-19 Championship, with the latter being held on home soil. France reached the semi-finals at the 2007 finals and lost in the group stage in 2008. Le Sommer later featuring with the under-20 team at the 2008 FIFA U-20 Women's World Cup, held in Chile. In the tournament, Le Sommer scored a team-leading four goals, which included a brace against Argentina in the final group stage match, which sent France through to the knockout rounds, where they faced Nigeria. In the match against Nigeria, with France trailing 1–2, Le Sommer converted an equaliser in the 49th minute. France later won 3–2 with a late goal from Nora Coton-Pélagie. Unfortunately, Le Sommer and France suffered elimination in the next round to North Korea. For her efforts, Le Sommer was awarded the Bronze Ball as the tournament's third best player.
On 12 February 2009, Le Sommer made her international debut in a 2–0 win over the Republic of Ireland coming on as a substitute. After appearing consistently with the national team, which including scoring two goals over the course of four matches at a tournament in Cyprus, Le Sommer was selected by coach Bruno Bini to play at UEFA Women's Euro 2009, despite the player not appearing with the team during the qualification process. During the tournament, Le Sommer played in all four matches her nation contested. France reached as far as the quarterfinals losing to the Netherlands 4–5 on penalties with Le Sommer converting her penalty shot. On 23 September 2009, Le Sommer scored her third international goal against Serbia in a 2011 FIFA Women's World Cupqualification match.