O.K., it is potentionally dangerous when it works and the only way you can know for sure if it works is to be hypnotized. And once you have been hypnotized, it is easier to hypnotize again. If you cannot be hypnotized, then none of this is of concern.

I tried to verify your one in five number, but I got higher numbers (three out of four). But, maybe we are not talking about the same kind of hypnosis. It is harder to find someone who can be fulfill a stage magician's requirements than to find someone who can be hypnotized in a quieter setting. One source even said 95% of people can go deep enough into a trance state to "benefit" from it. This number seems too high to me, but what do I know? Maybe that means along with some other relaxation method.

Shaela's family should have some videos of her (normal videos, not the one in this thread). Maybe they can show those to an expert and get an idea how susceptible she is to hypnosis.