problem with a coworker

I found out that a coworker I directly supervise has not been following the guidelines for her job. I have to have a meeting with her to address it and I find myself having thoughts that judge her. (It’s nothing ethically she has done wrong, just an approach to the job that is different than she was instructed to use and is now causing some problems). I don’t feel particularly comfortable in a supervisory role and I definitely don’t like the idea of having to confront her. Here is my model:

C: I learn x,y,z, about coworker and schedule a meeting with her.
T: She is a problem and now I have to address it
F: Angry
A: Judge her
R: Find more evidence for how she is a problem

I want to go into this meeting from a “cleaner” place, less judgmental, but I can’t think of any alternative thoughts.