My advice would depend on how willing this lady is to out herself by standing up to this bully, as well as the motivation of the ex-roomie.
Is the Ex just a plain and simple bully? Or is he/she on some sort of moral crusade, offended by what this woman does for a living and determined to shame her via outing for that reason alone? Or was he/she attempting to blackmail the provider and is now making good on those threats?
My own response would depend on which factors were in play, but personally.... I'd try to fight fire with fire. But that approach is absolutely NOT for everyone. ;-)