There are two issues here:
First, you are assuming facts without any support. All we have is a photo of her being hit in the fact by pepper spray. From that you want to draw the conclusion that she was animated before the fact. That is unjustified. Getting hit in the face with pepper spray justifies a substantial amount of animation—and there is nothing to suggest what she was like before.
Second, and more important is whether the actions by the police were necessary and proportionate. Even if she was yelling at the police and calling them every dirty name in the book their job is to be professional and to contain the protest and ensure they are not injured. As there is a gap between the protesters and the police it does not seem they were challenging the containment.
So was anybody in danger? The police were 2-3 rows deep in full riot gear including kevlar vests, helmets, batons, and pepper spray. The "largely peaceful" (see title of gallery) protesters were unarmed and the the woman was substantially shorter than the people around her. What threat did she pose to the police that would justify any use of force? Yelling at the police is not a threat.
As I stated earlier, people like the OP and yourself who say you do it and see what happens miss the point. It is like telling students at Kent State and Jackson state, "Why don't you stage a protest when the national guard arrives and see what happens." The abuse or repeated abuse of power does not justify it. Might as well tell the people protesting in Syria: why don't you go out there and see what happens to attempt to prove that Assad is right in killing 3,000+ unarmed civilians.