In August McCallum competed at the National Championships where she placed fourth in the all-around, behind Simone Biles, Morgan Hurd, and Riley McCusker. She also finished fourth on floor exercise, sixth on uneven bars, and fifth on balance beam. On August 20 McCallum was named to the team to compete at the Pan American Championships alongside Jade Carey, Trinity Thomas, Kara Eaker, and Shilese Jones. There she won gold in the team finals, all-around, and uneven bars and won bronze on vault and balance beam. She had the fourth highest score on floor exercise. Her all-around score of 57.000 during the team final was the second-highest international score in the world in 2018, behind only all-around champion Biles.