It's not simply the clothes which are exquisite, but also her carriage and her movement. To use a word I like, it is oblique.

She is aware of you standing here, but does not exactly acknowledge you. There is possibility, there is hope, but there is nothing definite, which is an accurate description for many people of the erotic.

The lack of jewelry, the cleanliness of the look contributes to its effect. Rather than noticing jeweled earrings, one notices the shine of her hair.

I would say it's the asexuality.
Today looking like that people would immediately categorize you - Lesbian, or something else, while back then it was a question mark. It was affirming you're a liberated woman. Liberated from the prison of femininity, and a feminist before it became a slur. At the time men also could have looked like that, while today that would be less popular. Both sides accepted the question mark of their sexuality, because everything was allowed. You would expect such a woman to have sex both with men and with women, and probably the same for a man who looked liked that, and that this sex would be seen as a liberated act rather than a categorizing one.

We just can't feel this freedom today, certainly not about our sexuality.

Indeed, there is a lot of ambiguity, which is well played. For instance she is in the middle of a gesture, but not a definitive one. We are not sure which way she will go down the street or what she is in the midst of thinking.

I also find the point about sexuality brilliant, I wonder what constrains our freedoms now, is it healthier or easier to have constraints to push against? Otherwise perhaps people do not know what to do, or they imagine the constraints are not there and therefore not worth fighting, simply because they do not see them.

The combination of the shoulder pads, which is a masculine or military touch, with the ruffled blouse is nice. I imagine the blouse is silk, from the way it drapes. Also, I find the detail of the shirt cuff extending just beyond the jacket to be beautiful. And the fact that we do not see her shoes, even though we understand they are heels, the femininity of heels would have distracted from the fine line between the genders.