It's a horrible thing to happen, and scary to think that it can happen to anyone. Even worse when they are still young and in the beginning of their adult life.
She said she can't recall when or where she would've come in contact with it, and I'm sure not knowing would make it even worse for her - but on the other hand she warns to everyone 'please don't feed the pigeons', so I guess we can assume that's what she was doing.
Anyway, Captain Hindsight will tell you that you shouldn't feed any animals who are not domesticated. They exist outdoors because they survive without human help. People do it just because they think it's fun and cute, whatever.