Something that may be useful if you are ever in a situation like that in the OP.
A person who is red in the face is in an agitated state but still in control of themselves. When such a person suddenly goes white in the face they have entered a fight-or-flight state filled with a rush of adrenaline and they are no longer in full control of their emotions – you are likely to be subject to in imminent attack.
When you see them suddenly going white in the face you should immediately take action, either disabling the attacker or getting away from them as quickly as possible. Do not hesitate; take immediate action.
Wait a minute. You’re recommending “disabling” somebody not for any action they took, but because the color of their face changed?
Maybe their face went white because they’re about to pass out. Maybe they went white because they just saw their boss in the crowd and they think they’re going to get fired. Maybe they can control themselves in that state of rage, and they’re about to back out of there. I don’t think your defense in court is going to look very good if it amounts to ‘your honor, I permanently physically damaged that person because it looked to me like they’d gone white in the face’.
If you’re recommending diving under the table at that point, that’s another matter.
And she’s an urban planner so it’s likely she’s faced a braying mob before, like many who work in a municipality, the public can get nasty in your face.
“If just one person comes up into your face and yells at you to do something that you have no desire to do, is that justification for violence, to break their nose or pepper spray them?”
Getting right up close, yelling and refusing to back off could legitimately be interpreted as threatening behavior that justifies a snootful of pepper spray, yes.