Katie is an amazing and supportive friend. Katie is the first daughter and child of Jennifer and Robbie Cooper, however, they divorced when she was 11. She has a younger brother Jack Cooper and best friend Alexa Mendoza. She lives beside the Mendoza's who are her family friends. Katie shaves her head for Alexa so that she doesn't have to go through losing her hair alone. She is a good person who rarely does anything bad. Katie gets anxious when she talks to people. She is super supportive and loyal and is always okay to try things she is scared of. Katie is a very independent person and a hard worker.
In the season, Katie visits Alexa in the hospital and was there with her when Dr. Bretweiser clears her for school. Katie finds out that Alexa started to lose hair and shaves her head for Alexa. Katie needs to buy a wig for school and is forced to buy a $300 and $50 wig after accidentally leaving the store with them. Jennifer tells Katie to return the $300 wig and they'll buy it next week instead. Katie refuses to tell Alexa about her money struggles and only mentions it when she's in line to buy Jack's video game. Katie decides to try out for basketball with the help of Alexa and Lucas, she doesn't make the team but now everyone believes her to be the girl with cancer when her wig falls off. Katie decides to be a "cancer girl" for Alexa and starts receiving gifts from people. Katie is forced to watch an R-rated movie with Alexa when Alexa believes she's ungroundable. Katie tells Alexa to go to the Wellard sign by herself and thought she would return soon. Alexa didn't return and Katie goes to the Wellard sign to meet her. Katie auditions for the role of Juliet with the help of Alexa and her stuffed animals. During auditions, Katie hears Vanessa calling her "sick girl" and she gets nervous, messing up her lines. She ends up getting the role which shocked everyone, even herself. Katie went to two rehearsals, the first one where she ends up throwing up from hearing whispers of people referring to her as "cancer girl" and wonders if she deserves the part. In her second rehearsal, Alexa comes to support her with Bernard, a stuffed bunny with judgemental eyes. Everyone stood up and clapped for Katie which stresses her out and she runs out of the room, followed by Alexa. Alexa reveals to everyone that she has cancer so that Katie doesn't have to go through it for her. Katie follows Alexa around as she pranks Gwenny. When Katie realizes that Alexa is upset from the fact that none of her pranks is affecting Gwenny, who she hoped would be mean to her in return. Katie begs Gwenny to be mean to her and Gwenny reveals that she's only acting nice so her reputation won't be ruined. Realizing only one prank would push Gwenny over the edge, Katie does one on Gwenny. A light prank that ends up being a horrible prank that causes Gwenny to rip Alexa's wig. Katie tells Alexa that she would stall the photographer by starting a fire. Alexa calls her mother to bring a new wig and Katie reaches her hand out for the fire alarm but Alexa shouts at her. Alexa decides to take her photo without her wig because she finally realized that cancer didn't own her and she was her own person.
- "I'm Coopie Kater!"
- "And who names their kid Jigsaw? I mean, those parents were asking for it - and they got it. Oh, and they got it again."
- "As long as I'm your best friend, you never have to go through anything alone."
- "I- I can call in a fake fire. I'll set a fire!"
- " Being cute and funny won't work here."
- "Life is better with Alexa."
- "The K and C keys didn't work so I had to sign off as Atie Ooper"
- "I'm a straight-A gettin' coffee makin' rock star-"
- "Be quiet or I will end you."
- "I'm going to be perfect tomorrow."
- "And this time, I don't have to dance around with a meatball on my head."
- "The hills were alive... but everyone else was dead so..."
- "Oh, so THAT can be huge?!"
- "I- I was thinking more like ice cream... With dangerous toppings!"
- "I mean you said 'Oh bejeez'"
- "Ryan, that shirt looks really good... on your body-"
- ”I am a hard worker”
- ”Wow so um, this is uncomfy so I’m going to go help Jack”
- “I’m goin’ to miss, you sweet, sweet weirdos”
- ”Just drink your perfect drink Sue!”
- ”Oh shoot I was supposed to clean the bathroom but I just decided that’s your job now haha sorry...”
- ”And then you pushed me!!”
- ”Ohh accept for that bunny with the judgmental eye!”
- “You would if you called him back.”
- Katie used to have a huge crush on Alexa's older brother, Lucas.
- When she was little, Katie had a crush on Lightning McQueen.
- Katie's parents are divorced.
- Katie, just as her best friend Alexa, has a huge crush on Harry Styles and wants him to marry her.
- Katie suffers from anxiety and has panic attacks.
- Katie still uses kid’s toothpaste.
- When she was little she went to a water park and her mother pushed her down a slide she was too afraid to go down.
- Both she and Alexa love Harry Styles and want him to marry them.
- Katie wanted her high school nickname to be "The Blizzard"
- She played the role of a fork in her middle school play, 'The Beauty and the Beast'
- When she was a kid, her mom let her throw a rock at the back of a bus on her birthday.