Diallo won her first major medal at the 2014 World Junior Championships in Athletics in Eugene, Oregon. She broke her own national junior record twice during the event, landing a 14.24 m jump in her first attempt with a 3.2 m/s headwind. After a foul in the second round, she jumped 14.44 m with help from a 3.3 m/s headwind, an attempt that was enough to win her the gold medal. However, these two attempts were not accepted as national junior records as there was too much headwind when they were made. Her fourth attempt of 14.20 was accepted as a national junior record, and also became the 15th longest attempt of all time in the junior women's triple jump. She became the third French triple jumper to win a world junior title for France after Benjamin Compaoré in 2006 and Teddy Tamgho in 2008.