If she's properly weighted there will be no issues on the surface. And unless the crotch strap is made out of really stiff webbing that statement is an out and out lie. The only time a crotch strap is noticed is on the surface or when scootering. You might feel it under water when swimming but no more than you'd feel wearing a pair of board shorts. A soft 2 inch one is what I use with just a bathing suit. If someone was wearing say a thong bikini it might be an issue but only a fool would dive like that anyway. Or a model for some photographer. Smart divers wear rash guards, skins, etc. BTW anything thicker than a skin will negate the irritation or even noticing of a properly fitted crotch strap. They just want to sell you what they want to sell. Not necessarily what is best for her. 
