Well I feel pretty well placed to say my piece as I'm not only a stepmum, I'm one of those weirdy woo-woo people - although plenty of mumsnetters will vouch for the fact that I'm pretty normal and certainly not about to have social services knocking because they're worried about Munchausen's by Proxy .
The arm bending is called kinesiology (which someone mentioned earlier), and I've just taken my child to see someone because the NHS haven't been able to get to the bottom of her problems.
It can grate when you're a stepmum and the ex is making demands on what goes on in your own home. And yes, it does smack of control over some issues. For us it was to do with where we were "allowed" to go on holiday, and for a time whether we were "allowed" to have dsd for special family events if they didn't fall on dh's weekend.
But I really can't see that the ex here is doing much wrong. She's a kinesiologist, it sounds like she maybe leads a very spiritual life. Those are her beliefs which don't have to be agreed with, but need to be respected. I think it's fine that stoat doesn't agree with the things her dss comes out with (I would have been on board with saying it's all ridiculous and just plain weird a few years ago) and her views are equally as valid - and she should be able to continue in her own home more or less as she wishes. There's absolutely no reason why she can't say to her dss "well your mum might think that, but I think this". I have lots of different opinions to dsd's mum and if any come up I just tell dsd that there's no right or wrong, we just think different things and that's fine.
Now the special food requests don't seem too bad to me. Dd has just gone off to a relatives for the weekend and I asked them not to give her anything with wheat in, which they didn't. However, if it's not being discussed with stoat and her dh in advance so they can get the right things, then I think the ex is being unfair. Whether she is doing it without discussion because she's aware of how stoat and her dh feel about the kinesiology, or whether she's just deliberately keeping them out of the loop I'm not sure. Sensitivity to chocolate just before Easter? - except I found out my child was sensitive to sugar (and therefore chocolate just before Easter too). But with the sensitivity to Turkey just before Christmas too it could be a case of her trying to spoil things when he's at stoats.
It just strikes me that if the 3 of them maybe talked a bit more, a it might help. Having said that I know that with some ex-wife situations that can be completely pie in the sky, and if stoat really believes that the timing of these sensitivities is to cause maximum hassle my best advice would be to rise above it, and never to let on to the ex that it has annoyed her.