Bring an attractive friend and have a threesome

jk.
But yes, if you are going there, bring friends.
Focus on
having a good time with your friends if you are there, do not focus on looking good for her, or trying to chat her up. Also, don't tell your friends you want to hook-up with the barmaid, they'll watch you when you end up talking, laugh and shit, it will make things akward.
On a further note, hot bar people get hit on a lot. Do not create a facebook just to get in touch with her. What you should do is pop up in the bars she works now and then with friends (both girls and guys) and have a fun time.
She'll notice.
Now personally, I have never hooked-up with a barmaid (atleast not one that I met during workig

) so I could not tell you from personal experience and this is now on my to-do list
Best of luck and let us know how everything works out for you!