It's extremely important to investigate any and all rape charges. It's important to treat all claims as serious until they have been properly investigated. But it is also important to prevent people from taking advantage of the gravity of these charges by holding them accountable for repeated false accusations.
A false accusation once? All right, everyone makes mistakes.
Twice? Maybe you should have learned your lesson.
Three times? Shouldn't some sort of charges be brought up against this person? Isn't this slander?
Rape accusations are serious. They are serious because they need to be. But to take advantage of this by ruining the lives of men with whom one has had a falling out as this woman did accomplishes two things: it acts effectively as slander, sometimes haunting the men for years after the fact, and it lowers the credibility of other women whose complaints are valid. Slander is a crime. False complaints are a crime. Why isn't this woman being prosecuted?