I'm not saying she wasn't poisoned, because I know there is a lot of poisoning going on in a general form and a directed form. I just doubt they would use Cadmium to do so
to answer the other question, if you are a successful healer and you are then poisoned it discredits your previous work as who is going to believe a sick healer? it is also a good way to test new poisons to see if the said healer is able to get rid of them
you can quantify with Dr Clarks synchrometer if, as I said, if you know how to use one to its full potential - things have moved on since she published her books