If someone is found innocent of a crime, and then new evidence comes to light proving her guilt, which protection applies?

The protection is called double Jeopardy its a procedural defense that prevents an accused person from being tried a second time on the same or similar case. As described in the U. S Supreme Court in its unanimous decision one of its earliest cases dealing with double jeopardy," the prohibition is not against being twice punished, but against being out twice in jeopardy".