I’d just roll my eyes at SIL. There are plenty of options for her to eat.
But, as a guest, inviting 4 other people to a family function? That’s just tacky.
Nowhere does the OP say SIL is expected to “forage for themselves,” she has been invited and asked to either “bring her own protein or eat the salads and other non-meat dishes people are bringing.” She HAS been more than adequately accommodated, just not to her satisfaction, and that is objectively “bratty” in my book.
Fair enough. That said, it doesn’t seem like it should be such a hardship to make do or pick something up you like on the way. I don’t understand why she would feel slighted when someone has already made the effort to reach out to her and let her know, “Hey, we’ve tried to make sure there’s something there for you, though please bring your own if you need something else,” particularly when the OP indicated that she’s never made an effort to host a gathering herself.
But to your point, we don’t know her side of the story. Not knowing more, if I were in the OP’s position, I’d be rolling my eyes in exasperation.
But in what sense has she been adequately accommodated? In terms of getting calories, sure, but in terms of being made to feel welcome there’s room for improvement. IMHO.
I don’t even like portobello burgers to be honest, but when people go out of their way to provide them at cookouts I always eat one and make sure to thank them. It’s a nice gesture.
That’s not at all what is described in the OP. There’s plenty of food that a vegetarian can eat. In fact, if I were attending a dinner at a true vegetarian’s house (not a pescatarian) that’s all I would be expected to be served anyway.
I prefer beer to wine. Some of my friends only drink wine. Sometimes they may have some beer on hand for me, but if I want to be sure I bring my own. I certainly don’t feel slighted if I am offered only wine.
Contrary to popular belief, we don’t just eat salads and sides.
So she gets to dictate the menu to the hosts? She eats fish. The host does not, so they have requested she eat the other non-meat dishes or prepare and bring her own fish. That is by any measure a reasonable accommodation. She refuses to do so. She’s the one making herself unwelcome, not everyone else.
If YOU are the person with the problem, YOU need to solve it on your own and NOT expect the rest of the world to kowtow to your personal choices. And if she’s feeling that unwelcome, she doesn’t have to go.
They’re the ones who invited her. You don’t find it all unwelcoming to say to someone, “Hey, come over to my house for dinner! But I’m making something I know you won’t eat, so bring your own dinner or make due with the sides.” I dunno man, you do you but I wouldn’t put a guest in that situation.
Maybe it’s just how I eat, but “sides” and “entree” is really pretty arbitrary. I don’t have any problem with the idea of making a meal out of a potato dish, a corn casserole, and a couple different sides. Why would that be “unwelcoming”? It sounds like it’s going to be a long buffet with lots of choices. No one is going to like everything, but everyone will have several things to chose from.
What makes something an “entree”? I am not being snarky–that’s a serious question.
When I invite people to my house I say, “This is what we’re serving. If you don’t want that, bring something else, or don’t come.” A reasonable adult does not then shoot back with, “If you’re not going to serve X, then I’m feeling unwelcome and I’m going to pout unless I get my way! Boo hoo!” And if they do, you’re god damned right they’re not fucking welcome.
When you decide “this is what we’re serving” do you take into account the pleasure and comfort of your guests? Or is it just whatever you’re in the mood for and damn their preferences?
“I’m gonna invite my friend Bob over for dinner, I know he’s lactose intolerant but I really like cheese quesadillas so that’s what I’m making. If he doesn’t like it, he doesn’t have to accept the invite or he can bring his own food.” That seem OK to you?
If you’re just going to keep throwing out extreme examples then we have nothing to discuss. But I’ll address it.
If Bob is the only one invited, of course not, that would be openly hostile and you know it. This is not that situation.
There are over a dozen people invited to this event, is the host supposed to serve everyone’s favorite individual meal because that’s their “pleasure and comfort” or should everyone not be a fucking child? Not everything in life is going to go your way. You can either suck it up and eat what’s there and have a nice evening, or you can prepare your own food and eat that and have a nice evening, or you can be a fucking child and throw a tantrum because you’re too fucking lazy and selfish to do either of those things. THAT seem okay to you?
It’s also a potluck where SIL refuses to bring anything, claiming she doesn’t have time due to her job. Despite the fact that she works only a few hours a week, while the others have full time jobs.
What you are describing is exactly “having to forage.” She has to try and pick out a meal from several side dishes. There is no meal for her provided. But there is a meal for everyone else provided.
If this were potluck, then I’d have a different opinion. People just bring what they bring and you make do. Foraging is just what you do at a potluck. But the OP describes people being told to bring things. It’s still a planned meal, and they are specifically not planning a main dish for the vegetarian, telling her that, if she wants one, she has to bring it herself.
That to me definitely seems like a slight. It’s like bringing presents for everyone at a Christmas party, but telling someone else they’ll only get party favors, and that, if they want something, they can bring their own gift. The whole point of bringing food is that you’re doing so for the other people.
The only reason I don’t conclude that the host doesn’t dislike SIL is the dementia issue, which is relevant. That said, if my mother had dementia and I knew this meant that someone else I cared about felt slighted by something she did, I’d try to make amends.
Spiderman asks why I should have to bring something. I don’t, but I would, because it’s crappy to make people feel left out. I’d even lie and pretend that the host told to bring it, just to smooth over feathers. I know what it’s like to feel like the odd one out due to dietary issues, and I would not wish that on anyone.
It’s not for me to judge whether SIL’s feelings are right or wrong: all feelings are valid. As long as SIL isn’t being rude about it, there’s nothing wrong with that.
I can’t comment on the other issues the OP brought up, because they seem to be painting SIL in a bad light, so I don’t know if they are really insisting that their family come, or if it’s just they asked and were told it was okay. My mom’s family started coming with us to our family dinners with my grandparents after a while, and it was entirely mutual.
How much money they have or what job they have is irrelevant in this instance, though I can see how expressing anger when you are better off than others might feel like not checking your privilege, and might be a separate reason not to like SIL. I do not judge the OP for not liking SIL, just that not liking them leads to less favorable interpretations.
It sounds to me like SIL has issues with feeling that the family doesn’t like her. Her own family had to bring a main dish. Yeah, that would bug me, too. The only thing is that I probably wouldn’t tell anyone about it and just put on a stiff upper lip. But that’s just because it would be more important to me to avoid any fights in the family.
That’s just what you do, unless they are so bad that it is impossible.
Well this isn’t about “favorite individual meals,” the point is that she’s family and everyone knows about her dietary preferences. As you admit, if she were the only one invited and they just decided to make chicken and ribs with some salad and sides that would be openly hostile. If there were 100 people invited I think you can excuse them for not being accommodating to a single person. But where’s the line?
I’d disagree that there’s any evidence of her being a “fucking child” and throwing a tantrum. Of course that would not be OK, if I have to address your extreme example 
Presumably she’s also a full time mom of two. I want to know why her husband can’t do any cooking. It’s his family, can he not make something?
Well, presumably, he’s a full-time dad of two (and I’d think has full-time other job as well since someone has to earn the money). I don’t agree with women having to do all the cooking (or social planning, or especially gift-buying). But I never really thought of “it’s his family” dictating cooking the way I really think it should with gift-buying. Though, of course, couples may decide to have one bread-winner and one homemaker and duties be divided accordingly for the most part.
Here’s a question - would any non-fish dish do for a main course? Or is it fish or nothing from the people who actually bring food? Because “fish only” is a lot narrower and more demanding than “non-meat only.” Though I do, as others do, say fish is meat, just of a different subgroup.
It’s not irrelevant at all. It’s a direct response to what you had just said. You said that, if you ever invite anyone over, you simply tell them what you are serving, and they either come or don’t. You specifically said you would do the very thing you now say is hostile. It seems now that you misspoke.
This post is also adding a ton of stuff that is not part of the scenario. No one is saying that the host must provide everyone’s favorite dish. And no one has said that the SIL was crying, throwing a temper tantrum, or even being childish.
In fact, it’s unclear to me what SIL has done that let OP know that she was unhappy. We just know she feels slighted. For all we know, this was just through the family grapevine, where she happened to tell someone who told someone.
We have no way at all to judge how upset SIL actually is, let along how she expressed this feeling. People just assume she must be doing horrible things.
This should be no big deal in either direction.
If I was hosting and serving the main protein potion of the meal and I knew one person ate no meat no big deal to throw a veggie burger or salmon burger on the grill along with the chicken and ribs. Small thing to do.
If I was the no meat person dang also no big deal. Buy something to bring if neither I or spouse can prepare something or just get by with the many sides available.
Do these people have a history of bad blood that they are looking to be annoyed by and to annoy each other?
what is presented for consumption is from the perspective of the host. If it’s potluck then it’s up to the host to coordinate what is brought. If it’s not potluck then it’s up to the host to produce food people will eat.
If you’re going to invite a vegan who is allergic to nuts and gluten then you provide food that fits the bill.