Big Nick Dudley
Nick
OK, it looks like virtually everyone has done the sadistic/sarcastic death route (at least I hope and pray they are sarcastic). I'll actually answer the question both seriously and with a plausible solution.
Wait for her to feed the birds once. Then go up to the old lady's apartment, and knock on her door. When she answers, CALMLY and POLITELY tell her that you are one of the other residents of the building, and explain NICELY that her feeding the birds so close to the cars creates an expensive bird poop problem, and ask NICELY if she would be willing to cease and desist doing such an activity in close proximity to the vehicles. Maybe try and come up with other (again, serious, not death) activities that she could enjoy that wouldn't be hazardous to the vehicles.
If you be a dick about it, she'd ignore you, and maybe do it more. However, if you are polite, and ask nicely, while explaining the dilemma her activity is creating (she might not even know that she's the cause of the problem), she might oblige (especially if you can find another time-killing activity for her).
The African-American gentleman across the hall already tried this. He went up there and the bitch just looked at me like I's fuckin' crazy.