In the following year Miller-Uibo won the 2011 World Youth Championships in Athletics with a time of 51.84, becoming the first athlete to ever hold both the U20 and U18 championship 400 m titles concurrently. She returned to defend her 400 m title at the 2011 CARIFTA Games, but was disqualified in the final. She also failed in her defence at the 2012 World Junior Championships in Athletics, trailing in fourth. She did however win 200 m and 4 × 400 metres relay silver medals at the 2012 CARIFTA Games. In her last age category competition, she won three gold medals (200 m, 400 m, 4 × 100 metres relay) at the 2013 CARIFTA Games and was given the Austin Sealy Award as the best athlete of the tournament.