The evidence that they did have was circumstantial, which isn't strong enough to convict anybody. There just wasn't enough evidence to convict her beyond doubt, which is what our justice system is designed to do.
Speaking of meatheads, Evan naturally runs afoul of Kermit's next door neighbor, the school bully Conan. Conan stomps his sneakers on Evan's feet and complains that Evan has just gotten the bottom of his new sneakers dirty. Conan avenges this injustice by pulling on one of Evan's sweater-sleeves. This is a good example of something to mention the next time someone defends this series.