As the usual defender of law enforcement and the justice system, I'm really at a loss here. Unless she was actually causing more harm than good, and I find that hard to imagine, I can't understand why this wasn't handled as a warning, or if they were really bent out of shape by what she was doing, why not issue a summons and cite her into court. The arrest seems over the top.
That said, in my experience in the system, dog wardens and animal cruelty officers often act in this manner, acting like their cases should be top priority for the system and taking things to the extreme. I recall one officer who asked for "no knock" arrest warrants for a group of teens who were shooting dogs with paintball guns in their neighborhood. He also showed up in the prosecutor's office dressed in full tactical kit, complete with vest, shotgun, flashbangs, etc. He was sorely disappointed when he couldn't find a single prosecutor willing to do more than take the case in for review.