Depending on the facts, there may be a basis for federal wire fraud or mail fraud charges. It is likely that there are state criminal charges as well, but the precise violations would depend on where the wrongful acts occurred.
Likewise, you certainly have a number of civil claims available, but these would be under state law.
I suggest that you hire a private investigator to track down this woman. Just because she refuses to return your calls does not mean that she cannot be located and served for litigation purposes.
You be able to sue the companies under a theory of quantum meruit, which basically means that they received the benefit of your services and should pay you for them. Whether or not this would be a viable theory would depend on the law of the state. But I agree with the earlier suggestion that it makes sense to coordinate any action with some of the other victims.
At a minimum, the Fortune 500 companies should be alerted to this woman's tactics.
This type of crime may well be of interest to the federal authorities. Have you contacted the FBI? My suggestion is to join forces as a group and consult with an attorney in the jurisdiction where the alleged wrongdoer is located. Although you can contact the companies that received the services the response probably will not be that they are willing to paying twice.
Of course, every answer is based on the question asked and requires a more complete context. This answer should not be relied upon to make a legal decision. Seek the advice of an experienced criminal defense attorney before acting. Law Offices of Raymond G. Wigell, Ltd. Defenders of the Constitution since 1975/ Aggressive Creative Defense Strategies/ Website: www.waaltd.com 24/7 call (708) 481-4800 text (708)218-0923