Hi,
Hmm doing pics on your mobile might not give great results, mobile phones usually do not have a high resolution, autofocus or zoom options. Plus they suck in low light. I do vids with my mobile and high res pics with a 5 megapixel camera.
I have a digital camera (Sony DSC-H1) with 12x optical zoom, that helps a lot in getting the pics without being too close.
Try to be touristy, act as if you want to take pics of an object that's in between you and the girl, but shoot her instead, no one will notice the slight angle change of your lens.
Go to events where people take pictures, like fairs or sports events. Then focus on the crowd instead of the event. This girl was shot at an event where the local police explained their work to the public. You might have events like that in your neighborhood, just read the local papers
Hope this helps!