My understanding is a little different. The prosecution lost the most damning evidence, a cut out from the guys shorts with DNA; and the perpetrator passed a polygraph. And still Clinton got her client to plead guilty. With a guilty plea there would have been no opportunity for HRC to "attack" the victim on the stand. 

The notion that Clinton had negative things to say about the victim comes from an affidavit in which Clinton did cite expert opinion about how victims in similar situation can be unreliable--the negativity was generic and not about this victim. It was just the hypothetical possibilities  that justify the evidence request supported by the affidavit.