Oh feck it, Silks. How awful.
I'd say that keeping calm and letting dh talk to her about it is defo the thing for now. If she gets a big reaction then it gives the signal that this is a good way of getting and maintaining attention (I'm not saying that that's what she's doing, but it doesn't get to be that aswell if you see what I mean).
Then, I'd get on to your GP privately and mention your concerns. And chat to people who've been through this kind of thing on here.
All you can do is be there, offer food and keep calm in front of her though that must be horrendously difficult. I wonder are there any books for younger children about body image so that you could offer other ways of looking at her body in a week or so.
I think I'd be straight on to her teacher too, just so you have her views and insights on the issue too.
You have been so aware of all of these issues, and you've done everything you can to manage them carefully with her.
Is there a pet she's fond of, or a pet she could be given responsibility for feeding for a while so she starts to think about food in a way that gives her control but makes her think about it in a different way.
Sorry, these are ramblings off the top of my head. We're here to back you up, no matter what.