Zwarthoed began playing ice hockey at age three with the youth department of VJB Smoke Eaters Geleen.

She developed in the club throughout her childhood, eventually playing on their top junior team, the Smoke Eaters Geleen II in the Tweede Divisie from 2011 through 2015.

The SDE roster already featured a Dutch national team player in Zoe Barbier, who had played the 2014–15 season with the club, and Zwarthoed signed alongside national team teammate Kayleigh Hamers to increase SDE's Netherlands contingent to three players.

[4] As of the 2022–23 SDHL season[update], Zwarthoed was the leading point scorer in SDE HF history, having amassed 139 points in 275 games, and also held the record for most SDE goals scored, with 66 goals.

She was a member of Netherlands delegation at the 2012 Winter Youth Olympics in Innsbruck, where she won a gold medal in the girls' individual skills challenge.