maybe trick her into coming up to you like carry a tic tac container and spill them and see if she comes to help you pick them up? act lost and ask her for directions? or maybe, if you can get up the nerve, compliment her hair or car. oooh, i know, borrow a puppy and take it for a walk. girls will come up to you for sure
if the lady is smiling at you and making eye contact she probably is already interested so get some balls and go up to her.