I agree with braziliron for the most part.
I would kinda use your peripherals to see when she looks at you (try and dress peacock so she does this often) and when you notice her looking your way, slowly turn your head and get some eye contact, and try to give a nice smile, not some perverted smile but a friendly one.
You need to hold the eye contact slightly longer than her, this is a MAJOR self confidence test for me. If you look away before her then shell think your cowardly and it will make the rest of your pickup awkward. However, if you hold just longer than her, it shows courage and confidence, maybe consider giving her a friendly wave something to draw her attention when your holding eye contact, and from there you can approach. Do this within the 3 second rule, otherwise you look like a creep, and your brain trys to talk you out of it. Just walk up and try a school related opener just to get her talking and you can handle it from there
