Well Nat, if the place she is working at, is a drop in kind of place.. like where you can just go get a coffee.... Go in and have a coffee.. say hi, how are you, hows the job.. Then say, hey, i really enjoyed our trip to the movies that time, you were great company, would you like to do it again sometime? Or we could go get and ice cream/coffee/burger if you like.. Or if there is some concert coming up, that you know she would like, say.. oh.. i hear so and so are doing a concert, and i really want to see them, Howabout you, do you like them? If she says yes, say.. well why don't we go together, i'll go see if i can get tickets...
That will give her the chance, if she is not interested, of making a polite excuse.. and then you'll know to look elsewhere without feeling stupid... and if she says yeah great I would love to, give me a call... then you are on your way!
If she doesn't sound too enthusiastic, and is vague, then take it as a no thanks and stop wasting your time... lots more pebbles on the beach
Good luck!