Lammie has been a part of the Mouat rink since 2015, when they were in juniors. Lammie was the alternate on the team at the 2015 World Junior Curling Championships, where they won a bronze medal. The following year, Lammie was promoted to third, and they won a gold medal at the 2016 World Junior Curling Championships. The next year, the team won the gold medal at the 2017 Winter Universiade. While the team was still in juniors, they won the 2015 Dumfries Challenger Series World Curling Tour event. Their gold medal at the 2016 World Juniors qualified the rink to play in the 2016 Humpty's Champions Cup Grand Slam event, where they lost in a tiebreaker.