Often, drama continues as long as you react to it. So the question is how to stop reacting, more than how to persuade her to stop. And whether it stops or you stop noticing because you're not reacting, it stops being an issue for you.

one of those, "you can't control the ex, you can only control yourself" principles that's sometimes hard to put into practice.

If you can figure out how to redice or extinguish your reaction to her, it'd be great. Maybe develop a pat answer for her demands, "she eats fine with me. She was not sick with me. I brought her enough to eat. You weren't there." Or maybe just, "I can't believe you any more, you've lied about this stuff too much" (oh NO... not that... those things might even escalate this).

Hmmm... what to say, what to say... How about nothing, and just make note in the calendar of the complaint, when the complaint occurred, what she was complaining of. Ask the daughter to make certain of the timing, and note HER answer... then put down what it is that the daughter eat on this calendar.

For you, keeping a health log for her is probably necessary anyways... and maybe you could keep a highlighter pen around to highlight the ones where you notice that the mother's report and the daugter's reports about what happened are different. It's necesssary to figure this out for the health reasons, and so if there's a discrpancy, it could become a problem and it's worthy highlighting so that you don't mistakenly base what you feed her in the future based upon reports that might have been in error about the timing of illnesses. Over time, you might teach your daughter to keep her own health log so that she will be able to note her own food issues and allergies, and by the time she's an adult, if there are ever any health emergencies, she'll hav ea lot to take to the hospital to help the docs figure out what might have caused the emergency.

Since she's too young now, it's worth keeping in the log.

So, start a separate calendar JUST for this... and when your ex or xFIL says anything, you just say, "thank you, I'll note it in the log", and you also ask your daughter for a description of stuff in case she ate anything or got sick at all when you weren't there... so the log is complete.

It turns this struggle into a (we know false) appearance of two separated parents working together to resolve their daughter's serious health issue. Sometimes acting AS IF something is taking place, it really starts to actually take place... so it MIGHT work? MAYBE... and if it doesn't, then you have a log of dates & times.

And if the principle of drama continuing as long as it has an effect is true, then turning this drama into a cut & dried log of events might reduce the effect for the ex so that she stops all the drama? It's worth doing anyways, even if only for the health issues... and if it has a side effect of reducing the drama, then great.

Just remember to have some pat answers for her reports and craziness... and maybe even keep the log nearby at all times so you can take it out and note what she says in the log while she's having her tirade at you.

When I did some customer service, I found that taking notes while people are having a fit usually calms them RIGHT down!

It might work. It's worth a try.