In the eyes of the officers her vehicle is a weapon. If she were standing in the street blocking traffic this would have played out differently. She is being detained and there is an agent I'm front of her car. It's possible she wasn't even looking where she was driving because of the two agents at her door.
She starts driving forward into the agent in front of her as he draws. He fires the first shot. Those are the events. The entire time they are ordering her to stop and the agent that fired was blocking her path.
I'm not saying it's right. No government authority is legitimate. There are plenty of criticisms to the approach they are taking.
Any armed police force would handle this situation this way. Protestors ought to be annoyingly peaceful. The Canadian truckers protest in Ottawa are the example IMHO.