May er she was very aware that if she turned up in a ££££ dress, it may have cost more than the bride’s dress and taken attention away from the bride.
Another thought struck me that maybe she listens rather than assuming she knows more than other people.
As for the wedding guests on Tatler, I’d say they do care what they wear. And they don’t have taste. That is just my opinion. In the suburbs of the nearest city to me, are small and very expensive boutiques. They are filled with heavily embellished, overly patterned and OTT clothes. Eg why have a small button when they can put on cameo buttons/why have three quarter length sleeves when they can add a ruffle to the bottom of them. They are not to my taste (or bank balance) but they stay in business. Many people think expensive equals better.
Kitty Spencer, like Meghan was, is exposed to stylists from all different walks of life. That is her trade, her world just as it once was Meghan. If they had any interest in clothes. they would have learned so much.