In 2015, Jermaine auditioned for the second season of The Final 1, singing Bruno Mars’ “It Will Rain”. After the regional auditions, the producers shortlisted her as a potential contestant and eventually moved on to the next round as one of the 12 girls in the final 24. At the Top 24 round as part of Group 1, Jermaine sang “Steal My Girl” together with Vanessa Devi, Shanice Hedger and Ruth Matthews as the whole group, and “Blank Space” in the solo round, and was sent through to the next round. She sang “Lay Me Down” in the Top 16 round and made it through to the finals, singing “A Sky Full of Stars” as a group of top 10 finalists and “Almost Is Never Enough” in the solo segment of the Identity round. Following the eliminations of Lou Peixin and Shanice Hedger, Jermaine made it to the last semi-final show along with Charlene Su and Odelle Sabrin as the final three contestants and as females.
On 4 October, Jermaine duetted with Jessica Sanchez, the runner-up of the eleventh season of the American Idol. During the same night, she sang her winner’s single, “Shine”, a song written and composed by Ken Lim. At the end of the final results show, she won The Final 1, becoming the youngest female winner ever at the time of winning, overtaking Farisha Ishak, who was 19 years old when she won in 2013.