So, do you agree that she did something wrong etiquette-wise, or am I the wrong one?
I think she should have excused herself. Crying in front of people is just going to make them uncomfortable. Not only that, but people feel helpless when someone starts crying and there's nothing they can do.
I have a story, though. Back in 1995 when I had been working at XX School for only a year and 9 months, we were working on the school play, which I had written. (It got such good reviews by the people who came that they begged us to run it for another week, but the kids AND the teachers were so tired we had to refuse. Also, three other schools that I know of begged for the script so they could do it too.)
Anyway, the teachers of each grade had to take turns supervising the children from their grade for two nights and you could watch one night. Except, one of the teachers in my grade was the pianist, so she was in the hall every night. No problem, the other teacher and I said we'd each watch one night, and we'd both be there on a third night so it was fair. No problem, right? Ha.
My colleague got HepatitisA and couldn't watch one night. So I went to the director (who was a head of department then; she became the principal later) and explained the problem: there was no one to watch my grade on the night I was scheduled to see the play. Having written it, I REALLY wanted to be in the audience at least once! And the director said, "Too bad, you can't see the play. Colleague is sick, so you have no choice but to supervise the children."
I went into the bathroom and started crying. The pianist saw me and came in. I told her what the director had said and why I was crying. She said, "What are you crying in the bathroom for? That's not going to help! Go into the principal's office and start crying! If you want something, you must be prepared to do what it takes!"
So I washed my face, calmed down just enough to make it to his office, went in. He said, "What can I do for you?" And I said, "Director said..." and started bawling! They were genuine tears, I might add, just delayed from when I was crying in the bathroom. And the principal said, "It's okay, it's fine, we'll sort something out." And he did! Another teacher said she'd watch my grade and hers, and then the next night I could do the same. So I got to watch after all.
That was a time when crying in front of someone proved to be advantageous. I would never do it to manipulate people, but I find that if someone is being unnecessarily harsh or refusing to listen to reason, tears seem to help their hearing to come back online!