I also have not had this same girlfriend the entire time, but several gfs as long as I have known the security girl.
In other words, you've only been dating. Much clearer!
Well, here's your advantage:
I have made subtle hints about liking her and she has told me and other people I am the funniest guy she knows.
Not sure what kind of subtle hints you've dropped, but hopefully they didn't affect your situation negatively.
In situations like this where you've known the girl for a lengthy period of time, it can be difficult to turn a "friendship" into a lay. Don't expect to succeed with this one girl. Remember, it's a one-time shot, and if it doesn't go through, there are plenty of other women out there.
One thing you need to do is isolate her from the other workmates. Ask her out for a cup of coffee. Then after you finish your coffee, immediately take her out on a date. Women usually need to feel as if they're progressing in a "relationship" before they go all the way. Use plenty of kino, and combine it with c/f.
Once you've got to the point of touching her, take her back to your place with some excuse (show her something, feed the dog, turn off the coffee pot). Sit on the couch and chit chat. Touch her hair, rub her shoulders, smell her neck, and the rest should write itself.
I cannot guarantee that the above is going to work for you. People who are well experienced with women can pull this off. Again, I will warn you, DO NOT put a lot of hope in being successful with laying this woman if you're inexperienced with moving a "relationship" quickly. Just have fun and enjoy the challenge. If anything at all, this will be a learning experience for you.