I agree with
@Bokanovsky to a great degree, but that's not everything. The best relationships are rooted in mutual sexual desire, but its even more than that. It's an energy and a tension. A resonance or vibration between people.
And it is very rare to find. I have experienced it instantaneously exactly twice in my life. First boyfriend in my 20s; first relationship after my divorce. Now other relationships have had plenty of mutual sexual desire, but at a different frequency, including both of my marriages.
And sometimes it is more prominent initially in one partner than the other. This has certainly been true in my second marriage. He was instantly into me (its very cool to hear him tell the story how we met....) and I took some time to warm up, although I found him very handsome at first sight, the attraction needed to take root and grow.
@jhonny9546 I agree with
@JoyDivision1990 on the subtleness etc. It is very subtle, so much so that many men miss it, others misinterpret it. I think it is instinctive for a woman to take inventory of her surroundings, as a safety/situational awareness thing more than a scoping out guys thing; but if a woman possesses a certain openness and pleasantness in her demeanor she will radiate that in her energy.
So I see it more as a general way of existing in space rather than an IOI focused at a particular man.
That is why my advice remains, make a move. Worst she can do is say no. Thats not a big deal.