OP, create a work issue that you have to have her take on...something plausible. Set up a meeting later in the week to discuss it...say around 11.
First thing, she'll do the leaning over thing again...and this time, she'll look at you while you're looking down her blouse, and when you stop looking, and look at her, she'll still be looking at you.
That's when you say, "uh, I really didn't need your help with this so much, but I have to tell you that I think you're beautiful and I always enjoy looking down your blouse, and would you do me the honor of joining me for lunch or dinner? Your choice."
You're welcome. Get a photo or you will be shunned here!