Kadic Bombshell - S4.E20

When Sissi's pen pal from Iceland, Brynja Heringsdötir, arrives at the school, all the boys swoon over her, making Sissi envious. When Brynja takes an interest in Odd, he ends up showing her the Supercomputer. While there, she messes with the computer despite Odd's pleas not to, creating a glitch in a program Jeremy is installing that causes every virtualization to happen in the wrong sector and prevents materialization. This becomes all the more problematic when William catches Aelita alone on Lyoko. When forced to choose between his friends and his new love interest, Odd initially stays with her, but decides that his friends are more important. After rescuing Aelita from William, they make up. As Brynja has not been told anything about the purpose of the Supercomputer, nor does it appear that she even cared in the first place, they have no need to perform a return trip to the past before she leaves.