I can tell you already that from reading your post, if you go in there to approach her you're going to flop. Why? Because you are worrying way too much about it. You can't decided that whether she will find you creepy or not if you go in there just for her.
You only know her to be in one place, and it would be creepy to try and find her outside of work. But there is a way to do so.
First, before I tell you what to do, you need to change your mindset. Go into that restaurant like you own it. Go in there and have a great surge of confidence inside of you. If you don't, let out some strong "YEHAWS" inside your head, or whatever gets you pumped up. Another thing to keep in mind is to not focus on her or anyone else in the restaurant. You are in there for your own personal enjoyment, not to try to get to an end.
Now, the best way I can see in getting this woman is by playing and teasing with her. When she asks for your order, avoid the question and play around with her. After a few minutes, tell her that you want to see what she's like outside of work and figure out when her break is. When she does tell you, that's when you can meet up and have a full conversation outside of work. Follow the steps up to the number close, and you're good.
Good luck, and may the force be with you.
"There is no better than adversity. Every defeat, every heartbreak, every loss, contains its own seed, its own lesson on how to improve your performance the next time." - Malcolm X