First, don’t approach her during peak times that would be counter productive. It is important to see her when there is nobody in the bar. It is also important not to try to seduce her when her boss is at the bar. I use to say that social pressure is an important parameter for those who want to be successful with women. It is in line with my isolation rule.
It possible that you can’t talk to her at her work place. In this case, you should know when she finishes her job. In fact, you have to adapt yourself to the situation and find a point of entry. For instance, you know that she comes back every day taking the bus somewhere. You know that she studies at the local university. You know something special about her life… Information is power. The more you know about her schedule, about her hobbies, about her personal life and the more likely you can find a point of entry meaning that you can find a reason for her to call you. For instance, you heard that she has an issue with her computer & you can fix it. The more you know about her and the better it is. The goal would be to give her to contact you and then you would give her your business card. Once you have given a reason to contact and you & once you gave your details, you have done your job. It is going to be easy for this woman to contact you even if she is shy.
Then, if she calls you or if she sends you an email, you know that she is interested.