I tend to agree with you to some degree, but I still put this on her head.
She did two things wrong: She refused to sign. She resisted arrest. This sort of thing reaches critical mass pretty quickly. The cops are like the Rain Man in the airport. Do what he says and everything is fine. Don't do it, and watch how fast things escalate.
The bulk of the responsibility is on her.
"Brooks was stopped in the 8300 block of Beacon Avenue South, just outside the African American Academy, while dropping her son off for school."
Key point. Looks like a case of BWOCS.