That is a good point; the DU poster seems rather capable of getting around without too much assistance, which suggests that she might be one of those "lucky" souls who, being able-bodied themselves, have a handicapped sticker courtesy of someone else. It's entirely possible that that was the focus of the bell-ringer's ire.
Thing is, I used to work with someone at the lab who had a handicapped parking sticker, and looking at him, you'd never be able to guess why. It was because he had some kind of heart condition where his heart would not pump faster if he was exerting himself--running, for example. His heart would continue to pump its normal rate, even though his muscles needed the additional oxygen that would be delivered by an increased heart rate. I suppose that I should have been a tad more curious about it, but I never was. No, he wasn't a lefty--actually, he was about as conservative as anyone on this site.