Connection to Lyoko

From Code Lyoko Wiki

Aelita has a connection to Lyoko, which is due to the fact that she has half of the Keys. This thus ties her psychically to the operating system of the Supercomputer, which makes it more difficult to materialize her, as well as making her life systems depend on the functioning of the Supercomputer, thus endangering her life if the Supercomputer is shut down or is on low power. However, this also allows her to sense things happening in Lyoko, aiding our heroes to prevent XANA attacks. Aelita's connection to Lyoko has threatened her life at times. In False Start, Aelita collapsed after Jeremie shuts down the Supercomputer (much to everyone's, including Jim's, horror). In Common Interest, it almost killed her when the Supercomputer's power source was running out. In this instance, it manifested itself as a series of heart attacks.

Her connection to the Supercomputer and the virtual world was presumably broken when her Keys were stolen by XANA in The Key.