You have another very serious weapon for the girls. Just explain how the short lighting (darker near side of the face which is turned towards camera) makes the face look more thin, when less of it is brightly visible, compared to broad lighting (darker far side turned away, with broad bright side towards camera). Showing two results side by side can have impact. Short lighting is standard lighting technique, and has serious appeal to the ladies when they realize it what it does for them.
There are exceptions, faces naturally too thin like broad lighting.
Too much ratio becomes contrasty and dramatic, which can have its place (grizzled old men for example), but can be excessively dramatic for routine stuff like cheerleaders. And too flat and even is a fault too, pretty dull. But a compromise, a bit of ratio, is always a good thing. Start paying attention to all pictures you see... movies, magazines, TV soap ads, etc. Look at the lighting.
For example, the Portrait Professional ad at right bottom of this page... Looks high key, nothing is dark, but stop and look at it. Two sides of neck. Two sides of face. Lights are not equal, and it is NOT flat. Shading shows shape pleasingly, and the face looks thin.
Oops! I realize now there are more than one of those.
I mean the one single good one.