You answered your own question.
Therein lies the answer. Charlene's clothes are made to fit her. Her body, her stance, style, preference, etc. She seems to be finally asserting herself, having passed through "Cutting Edge Fashionista" phase that I think she was more or less obligated to embrace. Her sister-in-law is renowned for her fashion sense and elegance (or was), however Charlene is totally different both in style and in beauty. What suits a woman like Caroline, watched and dressed by the best of the best all of her life does not suit Charlene.
Her initial wardrobe never seemed to fit her personality or, more correctly, the sharp lines of "fashion" swamped her completely. She looked like a dressed up Barbie Doll, and not a happy one at that. Any woman knows that if you feel good in what you are wearing you look good and I don't think Charlene ever did.
The first real move we saw was at her wedding. Her civil wedding attire with it's gorgeous colour and flowing palazzo pants hinted at a woman we were unfamiliar with, and from that moment on she has been steadily changing the way she presents herself. Gone is the fussy fashion and in it's place a style that seems to suit her well.
She looks so much more comfortable in her own skin as she creates her own style, an athletic figure dressed in soft, flowing styles and soft and feminine colours, little of which will be found hanging on racks in high end stores.
To me her haircut was merely the last step of her own private emancipation and I have to admit, I envy the gamine look especially when she wears those enormous diamond stud earrings!