I find that drug users are like gay people, they give off a subtle or not so subtle vibe. Not always obvious to a lot of straight(non-drug using) people, but having done them know the signs. Junkie do seem to have a certain way of talking and acting, like the look on their face or the way they talk(not even drug related or nodding off), as do tweakers. Sometimes I have my suspicions with people you'd never think, often in positions of authority. A lot of people on television too.
The main question is would she snitch on you? She might not be a junkie or even a pillhead. Could be a pain patient, real or imagined, or a pillhead. They have this belief of superiority over H users. Could be an ex-user of H or pills. Could just be the way she acts sober. Shit even if she does H she might try to cover her ass. Sadly snitching is all too common in the drug world

.
If safe, I'd first get to know her besides drug shit. Once you have a rapport, I'd start with mentioning things like weed, maybe shrooms or xtc if it seems in her personality, then opiate pills. They're more socially accepted, though a lot view psychedelics as bad. A lot of people view heroin as the worst shit out there. Maybe mention something weak like vicodin, codeine syrup or percocet? With codeine you could use the excuse that you listen to chopped and screwed music if you're into rap and aren't serious.
Or if it's like your personality, make jokes about drugs. Maybe say jokes like, "Damn my back is hurting so bad, I need some fucking heroin," "This job sucks! I need some oxy to pass the time," or something like that.
Maybe mention references to drugs in pop culture, like Kurt Cobain or the song "Hotel California"? Maybe use obscure slang that only a user would know?
For me this shit wouldn't be too weird, for I use the Hunter S. Thompsom technique of acting weird all the time so it's hard to tell

. People think I'm high when I'm sober and sober when I'm high.
Gauge her reaction.If positive, then gradually mention heroin.
BTW, why do you want to know if she does H? Better yet why would you want her to know? Just camaraderie at work, curiosity, a friend to get high with, to get new connects, or do you want to bang her

? Is she hot

?