In the "Age of Apocalypse" timeline, after Apocalypse's attacks on Russia, she is taken to the slave camp known as the Core located in Seattle, which provides energy for Apocalypse's empire.
In the "Age of Apocalypse" timeline, Illyana was never kidnapped by Belasco at all. It was believed she had been killed during Apocalypse's attacks on Russia, but she was actually taken to the slave camp known as the Core located in Seattle, which provided energy for Apocalypse's empire.