I don't know the answer to that. Perhaps she could be prosecuted under fraud laws?
If there are loopholes in the laws, maybe they need to be tightened.
But banning something isn't always the best answer. Religious freedom is one of the most cherished ideals in America. I am an atheist, and to me religions seem like a kind of scam.
In this case it is likely that most of Sylvia's victims will fight tooth and nail to protect her, just as the followers of a cult will fight for its leader. Occasionally a few will wake up, but most will go on thinking that they are getting a good deal, and I am reluctant to tell people what they can or cannot spend their own money on.
This may be similar to the prohibition of drugs. The cure could be worse than the disease. Woo-woo and drug abuse may be social diseases, but it doesn't follow that a ban is necessarily the best solution.
Nobody is saying we have to legislate against religion, and we don't even have to, to get psychics like Sylvia Browne to stop scamming people. Let her have her Novus Spiritus all she wants. But Sylvia also does a lot of other things that would stop, with just a slight modified legislation, or just an enforced one.
Often, the law is already there. Take the disclaimer that John Edward had to put up after all his tapings of Crossing Over - that is a clear attempt of circumventing the spirit(!) of the law. Just enforce the law a bit tighter, and no more televised fame for John Edward. You think he would have become as famous as he is today, without his show? Uh-uh.
Likewise with Sylvia. Her psychic readings are indistinguishable from what Ms. Cleo did. She also dispenses medical advice. Just two things that, if legislators were brave enough, could vanish. Where would Sylvia be without them?