All these stories are so good. Would you consider checking out
www.etiquettehell.com and making a contribution? I don't know anything
about the person who runs the site. I've just enjoyed it and think your
niece and The Ranger's relative would fit in nicely.

When I was working in health food, I learned a lot about eating
disorders. There's no doubt in my mind that these women are mentally
ill, but I still get a freakshow type enjoyment from reading the stories
where one is more outrageous than the next.

Bringing this back to etiquette. I wonder if one could invite the other
nieces and nephews without inviting the one who eats everything that's
set out and rifles through the cupboards for more. If you (meaning
everyone in general) had a relative who was in a serious alcoholic, even
if he weren't in a treatment program, it might be good manners not to
invite him to a gathering where alcohol was going to be served. The
explanation for not inviting (before or after the fact) might be a
simple "We were serving alcohol, and I know you have trouble with that."
The alcoholic would likely be angry, but there wouldn't be much he
could do about the honest answer, and the other relatives would understand.

Thus with the problem eaters. Don't invite them to buffets. If anyone
asks, explain "my neice has trouble with food." Say it with compassion
and no sarcasm. Don't argue; don't explain, but stick to your guns.
Everyone who has met your niece will understand. Your niece won't, but
there won't be anything much she can do about it, and it might bring her
a few steps closer to getting the help she needs.

--Lia