I ran Cross Country and Wrestled in high school without issue while on MDI and of course there wasn't any CGM. Sounds like you are responsible in testing so no reason you need CGM.
I think a lot of us old timers love CGM because we lived in the "dark ages" of technology for so long. I know I personally find it amazing that I have a tool that tells me what way my BS is trending and give me a feeling that I have a tool that gives me one up on this disease.
I have always been told I do not have a disease it is a metabolic disorder. And yes I was there in the dark ages as well. So I understand how useful it might be to have a CGM, but at the same time I can certainly understand Kelsey's reticence to have yet another piece of technology attached to her. Regardless of how useful her parents or endo think it might be. At the same time Kelsey is sure a heck of a lot more responsible than I ever was at her age. 10 times a day ugh I'd get the CGM to cut down on the sticks.
I don't have any advice on this - hopefully the others will be able to give you some. Best of luck. xx