Please can I try to help with a little background information?
In my very humble opinion, Anne's whole manner of dressing, from the clothes she wears and the number of times she wears them, and her unchanging hairstyle at all of her appearances, whether on royal duties or private (but publically viewed) appearances [such as Zara's wedding] can ALL be attributed to her background: the theory is as follows:
Traditionally, for generations, the traditional Upper Class English lady was, generally speaking, NEVER too interested in 'High Fashion'. Concentrating too much on what one wore was felt to be evidence of being 'self-centred' / 'slightly vulgar' / without 'proper occupation'. These upper class values extended upwards to the BRF.
This is not to say that the traditional Upper Class lady was not interested in fashion, she was, but really only in a 'quiet good taste way' and there is a world of difference between 'fashion and high fashion'. The 'unwritten rule' used to be that at the start of each calendar season, ladies used to visit their Couturiers and order outfits for the months ahead along the lines of 'I'll need x number of day outfits' (suitable for racing and attendance at weddings and summer outdoor events and the like). I'll need y number of evening dresses' etc etc. It was felt slightly vulgar (for some reason) to be more specific as to the occasion, such as ' I will need 4 day outfits for Royal Ascot'.
The one exception to this 'non-specific rule' was the dress the Couturier created in accordance with the Rules laid down by the Lord Chamberlain for the lady's appearance at Court. [note to myself; after several PMs I have received, I must get around to writing about Presentations and Debutantes sometime] Even the outfits worn today by the typical upper class English lady to the Royal Enclosure at Royal Ascot are never the height of fashion - the typical Royal Ascot 'look' is more about style than bang-up-to-the-minute fashion.
I have mentioned this as 'the unwritten rule' - it was quietly acknowledged but never admitted out loud until Sir Hardy Amies, who was one of the Queen's couturiers at the time [along with Sir Norman Hartnell] let the 'cat out of the bag' by mentioning this!
And as well as the Couturier, a Lady's milliner was VERY important. Hats were always worn in the daytime when away from home; if lunching out, you even did so wearing your hat!! And no lady would EVER be without her gloves: day time gloves were straightforward; white evening gloves were ESSENTIAL, often with little buttons to enable you to 'fold' the palm part of the glove back for eating; rings being worn UNDER the glove and bracelets on top of the glove. And colouring your hair was felt to be a complete no-no 'She's a bottle blonde / brunette ' was a popular form of derisory comment in the 1950's according to my mother. Thus, if the grey began to show through, you either let it do so, or sneaked off to a trustworthy hairdresser and had your ORIGINAL colour restored. [Are you starting to see parallels with Princess Anne?!]
After young girlhood, being too concerned with high fashion and appearance was felt to be a bit, well, suspect. Contrast this with the Continental lady's concentration on clothes and fashion. In particular, French, Italian and Spanish ladies took great trouble with their appearance and followed fashion very closesly. The Uppper Class English lady always used to have a slightly ambiguous attitude to the well-dressed foreign lady -something along the lines of a mixture of admiration and suspicion. [Mrs Simpson's concentration on clothes was always frowned on by the typical upper-class English lady, it being regarded (according to my grandmother, who remembered the abdication very well) as further evidence of Mrs Simpson's general unsuitability.]
The well-bred English lady might not have been very interested in High Fashion, but that is not to say that her clothes were inexpensive - couture was very expensive. However, it was regarded as an 'acceptable expense'. Well-cut tweed suits for the country and riding clothes and shooting clothes could 'go on for ever', [as echoed above by the Princess Royal] particularly as they were classics that never dated.
Staples of the English Lady's wardrobe included cashmere sweaters [particulary the 'twin set', good leather handbags [generally not Gucci or Hermes], leather brogue shoes for the country, Silk scarves [in which case scarves from Hermes WERE acceptable]. Day time clothes were invariably accessorised with a pearl necklace [either a single strand or a triple strand, NEVER a double strand for a lady [another 'unwritten' rule] with perhaps a good brooch. Evening wear was a chance to sparkle in [preferably heirloom] jewellery.
Princess Margaret, particularly in the 1950's, was the nearest thing the BRF has produced in the way of a 'home grown beauty' until Princess Diana came along. However, in those days, 'High Fashion' seemed to be centred around women of 50 years of age: dig out some pictures of Princess Margaret when she was in her 20's and notice how she wore clothes that were the same, broadly speaking, as those of her mother's generation. Princess Marina was highly regarded as a beautiful dresser, but then of course she was not home-grown English! The classic compliment to pay an English Royal lady tended to be to remark on the beauty of her complexion [as, by and large, typical female Royals were not particularly beautiful or for that matter wonderfully dressed [which is NOT the same as being dressed in couture]. Princess Michael and Princess Diana are two modern Royal Ladies who took a great deal of trouble with their appearance and both were interested in clothes in a way that the typical British Royal Lady was not - which is another reason why I think that both ladies were regarded with a certain amount of suspicion by the BRF!
Princess Anne's wardrobe has always followed these classic dress rules. Four or Five years ago, I can remember being very surprised when I saw a photograph of the Princess in an evening dress that I had seen her wear at a charity ball in 1977. In other words, the dress was about 30 YEARS old!
Micheal Rasser, the Princess' hairdresser, once said in an interview that when the Princess told him that she could still wear clothes made for her 20 years ago, he responded to the Princess 'well, you shouldn't'. He also reputedly tried to get Anne to change her hairstyle, as he found the 'wodge' at the front 'not particularly becoming'. Anne steadfastly refused to budge on this, and the 'wodge' remained ....although on one occasion I remember that she wore an evening dress with a pink houndstooth printed skirt and RED [not auburn, red as in primary colour red] streaks in her hair. This latter attempt was apparently her concession to 'being fashionable' but the fashion commentators in the papers were not kind [unsurprisingly, as the effect was bizarre, not fashionable] and Anne [perhaps mistaking the attacks on her as relating to her fashionable appearance, rather than her curious appearance, which she appeared not to acknowledge] showed no desire to repeat the experiment.
Hope some of this is of interest.
Alex