Casting describes her as someone "who was once the fun one in the group but now is the mom to a son she loves while juggling being the parent she wants to be with her very successful law career".
Additional description says that Katherine "is living the plight of every working mother. A loving mom, she's juggling being the parent she wants to be with her very successful legal career. And there's a frustration that comes from feeling like being good at one requires compromising the other. When she married Eddie, he was a successful musician. But now that she's the sole provider, Katherine is the one who has to be the rock star".
In the unaired pilot, Katherine was portrayed by Anne Son. When the series was picked up by ABC, it was also revealed that Son was leaving the project and that the role would be recast. On June 27, 2018, it was announced that Grace Park would play the role of Katherine.
Park's late cast is possibly the reason of Katherine's short cameo in the second episode, as Park had to film the scenes for the pilot.
In "Friday Night Dinner", Katherine's phone number is registered under the name "Katherine Saville" on Gary's phone. However, per the series' marketing, Katherine uses her maiden name, "Kim", as last name.
By the events of "The Rock", Katherine is 38 years old.