I'm going to go totally against the grain here but first, let me say that I too HATE the TSA. I deal with them regularly at both D.C. area airports (Reagan and Dulles) and I can say that my low opinion of them is warranted.
Anyway, as others have pointed out, the officers in the video are Police, not TSA. There is a TSA officer standing beside her and it appears that he's going through her bag at a secondary screening table. As you can see, she's been pulled off to the side and I bet they wanted to scrutinize her further. You don't see when the police officers arrive. They are already standing there when the video starts. Where they called because she was unruly? Where they just standing there anyway?
My thoughts are that she probably got mouthy and belligerent. It also looks like they tried to place her into custody and she resisted. That would totally warrant to use of force. But not excessive force. It could be that a) they bungled the attempt to put her into custody b) the force was totally warranted. We can't hear what she says to the officers and the threshold for mouthing off is lower at the airport. She is still facing "obstruction of justice" charges and the disorderly conduct charge has been dismissed. Interfering with the TSA screening process is serious business.
I don't like the way it looks like she's been coached by an attorney. She's got that "pouty, look at what they did to me!" face. They did pin her down. Beat up? Hardly!!! Was it done properly? I can't say. From the video it does look at bit rough. But police officers are supposed to trained on these things and not every arrest goes by the book. Especially when you're standing on a slippery tile floor and trying not to make a scene while the person is flailing around. He grabbed her to remove her from the screening table and tried to sit her down in the chair. They slipped and she landed on her butt. She wasn't "thrown across the room". And yes, the male cop seemed to be more aggressive than the two females. You can see that she resisted the entire time though. I'd love to sit in on their meeting with their supervisor.
And how long was the verbal exchange before they attempted to arrest her? I'd love to see the whole unedited video with sound.
Now, if I'm wrong and it's found that these guys screwed up, I will be the first one in line to condemn them. Cops need all the good will they can muster and jerks who screw up don't help at all.