I think that the "hearing aid" idea makes a lot of sense, and I remember seeing this when they aired a Charlie Chaplin marathon in the 1980s (and I had heard of a mobile phone back then... "the brick" wasn't even a thought). I asked my grandmother (now deceased) who told me that she might have been hit on the side of the head by someone or something, and agreed not to sue in exchange for appearing in a movie. She very well could have been smart-talking to the director, since this wasn't a "talky" and so it didn't occur to her that someone might make a big deal out of her being a smart-aleck some 80-90 years after the fact.

But for the record, I'm liking the "hearing aid" theory much better. But until we have time travel and can go back and ask them, all we have is theory, whether for or against. We can't support the concept of time travel out of this one shot, and we need to understand the world of movie extras of the time. This wasn't a casual shot on an ordinary street, it was a set shot using people who were specifically expecting to be on camera. To whip out a cell phone under those conditions would basically be an act of desperation to get noticed--if this woman was a time traveler, was she stuck? Consider the angle of the person doing the act, not simply your own perspective.