When good manners and eating issues collide

DISCLAIMER: Before I launch into today's diatribe, I wish to establish, from the outset, that I know that eating disorders are serious, and are an actual illness, not something to be mocked or dismissed. I also know that there are plenty of people in the world with incredibly frustrating, debilitating gastric disorders that wreak havoc on their systems every day. I know this because my sister is one of them and has been chronically ill for seven years. So I am not trying to make light of serious things, okay? That said, where has all the politeness gone? Several weeks ago I talked to a friend from law school about doing something for Chicago's Independence Eve (motto: "why have fireworks on the 4th of July like everyone else? We do it on the 3rd because in Chicago we like to BUCK CONVENTION!") I had thought it wasn't going to come together but then it did and all of a sudden there were 12 people coming over to my house for dinner. 12! So I got my 4th of July grill on, making the traditional burgers, veggie dogs, corn on the cob, veggie baked beans, and pasta salad with baby spinach, tomatoes, and feta (okay, so that one isn't on the menu at Grammie's in Kansas, but I took some urban liberties with the tradition). I plunked some Cat Stevens on the stereo and waited for the guests to arrive. When my friends arrived, they brought with them a girl I'll call "annoying girl" (AG.) AG works at the same law firm as my friends. She talks. A lot. A lot of the talking somehow makes reference to her being fat. I start to get suspicious, because girlfriend is TINY. Then it's time to eat, and everyone goes through the line, taking corn and beans and burgers (side note: I have approximately 14 extra ears of corn and 7 pounds of pasta salad left over if anyone wants to come to dinner at our place tonight.) AG, however, does not go through the line, and instead shaves the tiniest sliver of cheese I have ever seen off the block of cheddar I'd set out for the burger eaters, digs into her handbag, and brings out a ziplock bag full of RAW BROCCOLI, which she proceeds to dump onto her plate and bring to the table with everyone else. Then, she goes BACK INTO THE HANDBAG and brings out a four-pack of screw top chardonnay, describes it as "bone dry and totally unsugared!" in sort of this gross chipper way, and proceeds to chow down. Now listen. If you want to bring your own broccoli to a party instead of eating the food that's being served, I feel sorry for you, but that's fine. My sister, for example, keeps one of those energy bars in her handbag in case she can't eat whatever people are serving, which seems totally reasonable,(and also a little more subtle than broccoli, but whatever). But don't you think that it would be courteous to alert the host to whatever it is that's compelling you to do that? I don't mean she should have given me the whole lowdown on her Atkins fetish or sucrose allergy or whatever it was at work here, because I respect people's privacy. But it seems like if I was in her place, I'd have at least given the host a little "heads up, I've got some pretty severe dietary restrictions so I brought some of my own food because I didn't want you to have to make anything special on my account." Right? Is this asking too much? Because let me tell you, there is no better way to get a group of 12 people to play "guess my eating issue!" behind your back than eating a plate of broccoli for dinner without so much as a word of explanation.