Model the behavior you're seeking and see if she follows.
Wear a set of headphones next time you go.
When you make eye contact with her and she smiles back, stay right where you are and take your headphones off to indicate that you're willing to interrupt your work to talk with her.
If she reciprocates, then you have your chance. If she does take off her headphones from this approach, keep this chat brief unless she seems obviously eager to continue. Start with something complicated like "Hi. My name is {say your first name}" Measure her response. Everything you say after that is on you.
If she does not take her headphones off, then perhaps try again some other time; she might not have time for a conversation at that moment. But realize that if she doesn't open up for something as innocuous as a "Hi" then you have to come to grips with the fact that she's just not into you.
If you try a couple times and she never takes her headphones off, move on.