The level of the "victories" do vary. But, in this particular case, I think a mass expression of support for this girl could actually encourage the local DA and school reconsider moving forward with prosecution.
Most of those victories can be chalked up to "post hoc ergo propter hoc."
It's hard to prove causation in any of these.
I had a few altercations with my high school administrators. The first involved a student petition, the second involved formal letters from attorneys. Guess which one had more effect.
Edit: nevertheless, I have signed the petition in question.
I say this not to tease about the goals and causes, but just that sending individual, targeted letters to the parties involved or a dollar to the family for their legal fund would do so much more. Internet petitions do nothing and are easily ignored.