Your credit reports are drawn from three different credit reporting bureaus. To get incorrect information removed from their files, your friend will have to get a copy of their credit report from each bureau and begin the task of disputing any fraudulent charges against her accounts. By law she is entitled to one free report per year from each bureau. From here she can begin to repair her credit.
As to what she can do in the mean time, I think she will have to negotiate with the rental companies on a case by case basis. But she will need proof that her credit was stolen. Otherwise they're going to go by the word of the credit bureaus. See the link that provides links to the three credit bureaus.