I agree with what you say, Mike, but let's face it, most portrait artists aspire to capture a sitter's individuality, so why dictate their wardrobe? Especially when you're moving the client AWAY from individuality, to make them fit the mold.
I'm in favor of parents being parents, but a portrait is a special expression of a person's identity. If the girl wouldn't wear a white linen dress on a bet, why portray her in one? This is an opportunity to strike a chord with the family and make a portfolio piece that stands out.
http://www.portraitartist.com/barth/redhead.htm
http://www.portraitartist.com/banks/blond.htm
http://www.portraitartist.com/mickle/sailboat.htm