Nothing is known about Katy's life before the apocalypse, except that she had a mother, and her father was Richard.
After the outbreak began, Katy was traveling with her mother and father until they found refuge at a tent city. Disaster struck when a fire and fight broke out, leaving her mother dead in the chaos. Three days later, Katy herself was killed right in front of her father, presumably by zombies. Since her death, Richard kept her backpack in memory of her.
Katy is mentioned by Richard to Morgan, when he reveals his backstory prior to arriving to the Kingdom.
Although her reason of death was never explored, it can be assumed she was devoured by walkers, due to her father saying "she died right in front of me."