In July 2017, at age fifteen, Smith competed in her first major international meet at the 2017 World Aquatics Championships. She qualified for the women's 200-meter backstroke event final and finished 8th. In August, Smith won gold medals in the 100-meter backstroke and the 200-meter backstroke at the 2017 FINA World Junior Swimming Championships. In the 100-meter finals she broke Missy Franklin's 15-16 national age group record, as well as the world junior record previously set by Taylor Ruck in the semifinals. She was awarded the 2017 National Age Group Swimmer of the Year for 15–16 year-olds.