That's a really good point, mathanxiety, but there is a certain amount of evidence you can pick up from reading between the lines.
For example, the fact that the foods this child has 'allergies' (okay, 'intolerances') to/with seem to change on a very regular basis. I personally don't know of many serious allergies which come and go with that kind of frewquency - but I do know my mother did a similar thing to herself, constantly cutting out this food or that for a few weeks. I can honestly say that on not a single occasion did cutting out milk, or flour, or potatoes or whatever it was make the slightest bit of difference to her health.
I also know that my mum treated my dad with utter disrespect when it came to our medical care, and used to just plough through fad diet after fad diet in an attempt to get my 'obese' brother back in shape (medically he was never more than 'overweight'). She never took him or herself to a doctor or shared her concerns with my dad, because she had nothing but mild contempt for my dad, and a deep mistrust of what the doctors would say.
Most alternative medicine practicioners actively discourage seeing a doctor for most things (or have IME at least), so it's unlikely the mother would have taken the boy to an independant specialist anyway, and has made the diagnosis herself.
She clearly is sharing information on the treatments her son is being sent to the OP's house with, but not in a two-way sense. It's just a case of 'I have made this descision regarding my son's car; you have to stick by it.' My mother did exactly the same thing for years. Frankly, at points my dad was too worried she would try and withold access to kick up a fuss.
I'm not saying this definitely is the case, but some biological mothers really are very manipulative towards their ex-partners. Particularly if they feel the father 'only' has to be with them every other weekend, and therefore has little influence.
Also, bringing up the fact that the OP is living with a man still 'legally married' to his wife is utterly irrelevant. Divorce proceedings often drag out to ridiculous levels when one partner is being difficult (I know my parents' did); to be honest, that has absolutely no bearing on the fact that the OP lives with a separated man. I know you probably didn't intend it this way, but it does come across rather like you're trying to bash the OP for being grasping or something.