Wennerström's junior career sent her to four straight World Junior Curling Championships, from 2003 to 2006. At the 2003 World Junior Curling Championships, she was the alternate for the Swedish team skipped by Stina Viktorsson. Wennerström didn't play in any matches, and the team finished 4th. At the 2004 World Junior Curling Championships, Wennerström played lead for Viktorsson's team, and they improved on their 2003 record, by winning the bronze medal. At the 2005 World Junior Curling Championships, Wennerström was promoted, this time to play second for Viktorsson, and they had even more success, winning the silver medal, after losing in the final match against Switzerland's Tania Grivel. The team would return to the World Juniors the following year, however at the 2006 World Junior Curling Championships, they could not improve on their record, finishing 8th overall.