I understand how you feel, but keep in mind that every life is a universe. Each person that exists, exists in their own world, with it's own set of problems, family, friends, happiness, sadness, etc. She is a person, just like you, she puts her pants on one leg at a time, just like you.....so don't let it build up too much. If you were to speak to her and she wasn't interested, you can't take it personal because you have no idea what's going on in her life.
The best approach is the casual approach. If she is as attractive as you say she is, she's probably has a lot of guys hitting on her. You'll want to stay away from the obvious and do or say something that stands out. If she's got amazing eyes, don't tell her that because everybody she meets probably tells her that. Tell he you like her necklace, or her shirt, or her ring. Ask her what kind of perfume she's wearing. Ask her if she enjoys working the front desk or does she hate it. Ask her if anyone has given her any problems. Where she is from. What she's majoring in. If she wants to get a coffee or something when she gets off work.
If you can make friends with her, that can lead to exchanging numbers, hanging out, etc. If you can get to that point, it's possible for it to go further, as opposed to asking her out right away and getting rejected. Then again, if you're not interested in making friends with her if she won't date you, then just ask her out for coffee. If she says yes, she might be interested. If she says no, ten she's either not interested or otherwise involved.
I welcome your thoughts, let me know if you want to talk more