Yes but not in the little girl's favor. Unicycling favors taller people and taller seat-to-ground height. The larger the distance, the easier it is to balance and maneuver.
This is a very good point. I have observed that people tend to forget the physical differences between being small and being tall. Not everything is proportional [1].
This isn't the worst thing in the world, but I hope it'll be helpful to know that the "Uhm" can come across as condescending. It seems to suggest that it's obvious or that someone not considering it is stupid.