The ID has everything to do with it. The cop asked to see it and she refused. That is why things escalated. She was not compliant at all throughout the entire thing. The cop reacted to her stupid actions.
So much this. No matter how hard the OP is trying to bait everyone, the police are clearly not in the wrong here. The initial reason for the stop, or her job are both irrelevant. She refused to identify herself, refused police instruction after several warnings about the result of such behavior, and then resisted being handcuffed.
The police at that point have no other choice than to take her to the ground and restrain her. They have someone who, for an unknown reason, is fighting them. They don't know if she has a weapon, is a wanted felon, etc. They are in a roadway with someone who is intent on fighting them. The quickest way to defuse the situation is get that person handcuffed.
Again, all of this would have been avoided if she had simply produced identification after being stopped for breaking the law. She chose tomescalate the situation, even after being warned as to the outcome of that behavior.