If you are correct in that this event was open to the public on a first-come first-served event, providing she wasn’t causing a disturbance, I would think Mr. Sanders may have a “problem” on his hands.
Hopefully, someone has a cell phone video of the confrontation and she could seek redress against the campaign under Federal statutes as a violation of her civil rights. Since she is a female, I believe she is part of the “protected class.”
Hopefully, someone with a law degree will chime in.
I wonder if notoriety, or a 'facial recognition' program was employed.
Nowadays, legal protections haven't kept up with the internet, or FakeBook.