Being a stylist requires a very nebulous sort of skill set. Someone "qualified" that can pick and follow the trends may very well be absolutely of no use whatsoever if their client is not shaped like a model.
The knowledge of their client and the various types of events she will be required to dress for is essential, as are the dictates of socially acceptable standards. My niece can pick a limp rag off a rack and when it is tried on it is brilliant, yet never would I have given it a second glance. Not surprisingly she is our default "stylist".
You only have to look at QEII stylist who started out as her dresser. Over the years, she has got to know her, her likes and dislikes, what works for her and what doesn't, and what accessories she wants and needs.
Finding that sort of person for a younger royal is very much harder I think because it requires them to totally subjugate their own personal likes and dislikes and concentrate only on what's best for their client. Often when you see a royal wearing something that you know you should like because it ticks almost all the boxes, but you don't. And the reason you don't is that the box it didn't tick is the wearer. It is not their style, not the type of ensemble you see them in and they don't look very comfortable.
Diana, strangely enough, had pretty much a free hand from the outset. HM sent her someone to advise, Diana sent her back. People forget that the ghastly aqua polka dot tent with a big collar that she wore when she left the hospital after the birth of William, was actually on trend for that social strata. The fact that it was the 80's explains the rest!
