Is there any evidence that the girl backed down instead of making her story up?
There's two things that stand out.
1 - Her actions and behavior are far more consistent with an abused partner than they are with a malicious liar.
2 - Her story was consistent with a pattern of abusive and hostile behavior that has been attributable to George Zimmerman from multiple sources.
He's innocent of that crime because he was never convicted of it.
Just like OJ, right? Just because he successfully thwarted a conviction in court does not mean that he was innocent. It just means that the government cannot punish him. People get away with all kinds of things that they're guilty of.