I do understand your fear about speaking up. One possibility *might* be to send her an email (using your work accounts). Something very polite: "Lately I feel you've been flirting with me. I'm truly very flattered and like you as a person. But because we're work colleagues, I'm just not comfortable with the situation." Et cetera... There have been just a few times when something really pushed my buttons at work and I sent a very polite, "positive" email to my group/bosses, sort of thanking them for all their good behavior and consideration toward me, but nevertheless expressing my concerns/pushing back. I didn't put any *threats* about going to compliance. Those emails were effective--at least for my situation.
The email will serve as *evidence* in the worst case. It could be good to have the situation documented.