Like any other approach but saying "caught you at the wrong time" (with a smile) if she's eating, shows social intelligence.
Most girls stop eating for a couple of mins.. after she has hooked, saying "it's ok, you can continue" (authoritative tone helps) again shows social intelligence and reduces social pressure, awkwardness and builds comfort. I read somewhere that people bond faster over food; I think it's evolutionary
If she's wearing headphones and walking, I rarely approach but if she's stationary, I'd say "you must like that song very much" (actually this doesn't matter cos she wouldn't have heard what you said) but after she removes her headphones and asks what?
You can repeat the same and when she asks why? You can either tease or compliment, depending on your style/personality
Same goes with anything, just use the opportunity to open and use social intelligence and build on top of that opportunity to hook her.