People do board the wrong plane all the time. One of the reasons they make announcements of "this if flight XYZ to ABC" is so that anyone who has boarded the wrong plane can hopefully figure out they're in the wrong place. I've witnessed it a couple of times over the years, so with over 20,000 commercial flights in the US every day, I wouldn't be surprised if it happens on a daily basis.
As far as the OP, I don't see what the fuss is, unless she was sitting in your seat. Confused and clueless people are in abundance at airports.