Katherine Pryde lived in the suburbs of Illinois and kept her mutant abilities a secret. When Apocalypse began gathering mutants, Kitty's parents were surprised to find a team of Infinites at their front door ready to take their daughter away. Her parents protested and were murdered. Kitty phased out of the house and ran.
Kitty became the youngest member of the X-Men. Magneto left her training to Weapon X, who was secretly preparing her to become the X-Men's ghost assassin. Given metallic claws similar to Logan's, Shadowcat took to her training readily. When Logan and Jean Grey left the X-Men, Kitty lost her mentor and began to question her role on the team. Searching for someone to bond with, Kitty turned to Colossus. The two developed a strong relationship and eventually married.
After a battle during which Colossus was frozen, the two of them decided to retire from the X-Men. Magneto offered a different solution, asking them to train his next generation of mutant warriors. Kitty wanted to walk away from the X-Men altogether but her husband accepted Magneto's offer.
During one training session, Magneto arrived and asked them to go to the Seattle Core and free a mutant capable of time travel. This mutant was Colossus's sister, Illyana. Shadowcat and Colossus sent their students to find Illyana while they secretly phased in the back. They found Illyana but were discovered in the process. Colossus chose to leave his students behind and commanded that Kitty phase the three of them out of the Core.
Realizing her husband had become obsessed with saving his sister, Kitty started back for her students. Colossus refused to let her go and told her to take Illyana to safety. Colossus returned hours later - alone. Shadowcat believed her husband may have betrayed his students and left them to die in order to reunite with his sister.
Colossus and Shadowcat delivered Illyana to Magneto. When Colossus discovered that Magneto planned to use Illyana to change their timeline into one where his sister was dead, he became enraged. Kitty, believing her husband would never hurt her, stepped in front of him to calm him. Instead of phasing she stood her ground and Colossus crushed her to death.