First, be absolutely sure of your facts.  You are getting into an area where you could be liable for defamation if you are accusing her of criminal misconduct and are wrong.  There may be other explanations for what you find to be a little shady.

There are two potential legal issues.  The organization may be violating the charitable solicitation registration act of your state (if there is one) if it is misrepresenting the purpose for which it says it is soliciting.  It is not entirely clear from what you have said that this is actually the case, however, so tread lightly with any complaint to the registration officer.  If she is stealing from the organization, the state Attorney General or the local prosecuting attorney might be interested but you would probably need pretty good proof and would probably have to be talking about a significant amount of money.

As I have said many times, the media may be the best enforcers of the law and ethics of nonprofit organizations.  If she has been misleading the media about her illness, they might be eager to expose her as a fake.  But if she has a different illness, it may not be as much of a story and most people are reluctant to attack a person who is seriously ill.