Ok, sorry. I maybe shouldn't have said that, but you said you didn't want to come across as an idiot. If she's that good of a friend, it won't hurt the friendship if you openly and honestly ask her how she feels. In fact, chicks dig open and honest.
Now, one last thing. You said you work with this girl. Do you work closely together? If you do, I would really recommend not saying anything, unless it's a job that could be easily replaced for you. Relationships at work can become very tricky very fast.