Katie is the main antagonist in the novel The Suitcase Kid. She is a step-sister of Andy and often bullies her.
When Katie is just a little, her mother dies. Katie hasn't already known what "death" means so they tell her that her mother "fell asleep". Unfortunately, it terrifies Katie so much she is scared to go sleeping. Since then, she does everything to avoid sleep at night: eats and drinks much, watches horror movies and wears the most unpleasant sweater. At first, she shares the room with her older brother Graham and always forces him to play games, so no one of them will sleep. Graham, unable to resist, is bullied by Katie all the time and she even hits him with a flashlight once.
Later, Katie's father Bill meets a new partner, Carol, and they get married. However, it also means Carol's daughter Andy from her first marriage will live with them, too. Katie is forced to share the room with her, much to her anger. It is only for every second week, as Andy also lives with her father.
It is a horror for Andy to live with Katie who taunts her all the time. Katie calls her "Andy Pandy" and often watch DVDs with him on her own TV, only to make Andy angry. She also makes fun of Andy's beloved plushy rabbit Radish and says that her parents don't want her anymore, because they have both new partners and children now.
Andy sometimes has enough of Katie and simply punches her. It always leads to one thing only: Katie starts screaming hysterically and makes such a big scene Carol punishes Andy for "bullying" her weaker sister.
Andy also minds Katie's strange behavior at nights, as she can't sleep well then, too. Graham later explains her what happened to their mother and how scared of sleeping Katie is now. Andy promises not to taunt her step-sister for that, although she often wishes to. However, when Andy decides to leave the house in the middle of the night to find Radish she lost the day before, and Katie wants to tell parents, Andy threatens her that she will tell them about her fear of sleeping. This forces Katie to be silence until Bill and Carol discover Andy disappeared.
As Andy later says, her relationship with Katie gets better a little bit after that, although Katie gives her a statuette of Andy Pandy for Christmas.
- Katie is five days older than Andy, but is smaller than her.