Forget your Watch

It's an old cliche, but it really does work. Forget your watch, and if she has one one, ask her for the time. Explain whatever it is you're trying to get to, so that it's not just a "what time is it?" and a run off. Don't make it a long, drawn out conversation. Your aim isn't to talk to her for hours, it's just to make you a 'comfortable' part of her life so that the next time you say hi, she recognizes you.