Do you think she actually likes me or that shes just trying to sell her drinks?

My guess is she is trying to sell her drinks. It's her job and she is at work after all. But you never really know and you don't want to let her slip if there is a chance and you probably don't want to do anything that would make you decide to never come back either. So I would suggest something lower key. This Friday why not say the following when she offers the shot: "I'll buy one if you do one with me, I'll buy!" She will probably say she can't cuz she's working blah blah blah. To which you reply "Then can I buy you drink after you get off work?" or Can I buy you one another time? That should gauge her interest in you and if positive ask "Great, when?" you can take it from there with getting the time, date and phone number. If she's not interested then she will say she has a bf or can't date customers or has to wash her hair. If she can take the shot, then buy her one, do the shot together and say something like "We should do this more often!" If she agrees.... you know what to do. Good luck!