I'm a bartender/waitress. I don't ever flirt with my customers, but my smiling and laughing may come off like that. I tend to my customers with a positive attitude and usually with witty jokes, if it's the right crowd.
I can understand that a usual customer might find that because she can remember your "usual" drink, or because she knows you always order an appetizer after your second beverage, it must be an interest... right? Not really.
We like to be efficient and give you a pleasant experience while with us; that's how I am, at least. If you think she is flirting with you for a relationship, then ask her when she gets off one night and feel out her reaction.