Taking this from another view point, has this person ever sat down and explained their condition or what the chemicals can be used? It seems unreasonable that they void everything without any explanation or their condition.
I personally do not think it would be an invasion of privacy to expect this person to explain what they can handle.
All you are simply trying to do is find a situation that works for all not just one. I think if they are not willing to at least meet and explain their situation then I agree with whale and call their bluff
Good Luck