Iwasa made her debut in the Continental Cup on March 9th, 2011 on the Zaō-hill in Yamagata and finished in 29th place. On September 28, 2013, Iwasa took third place at an FIS jumping event in Râșnov, Romania, and won the day the following day. In January 2014 she could not qualify for the World Cup jumping in Sapporo . With a reduced starting field, she finally made her World Cup debut a week later in Zaō and finished 42nd.
At the 2017 Winter Universiade in Almaty , Iwasa won the gold medal in the individual competition ahead of Yuka Kobayashi and Marta Křepelková , in the team competition with her compatriot Yuka Kobayashi against the Czech Republic and Russia and in the mixed competition with her compatriot Naoki Nakamura in front of the Czech Republic and the second Japanese team.