I can relate to this situation, and for all those out there who say that the child should be forced to 'eat something else or go hungry', or the parent should somehow 'find' something else for them to eat, well, WALK A MILE IN MY SHOES. I have a 2nd grader that *still* eats only peanut butter sandwiches for lunch every single day (no jelly, even.) The year she was two, I almost pulled my hair out in frustration, because she insisted on peanut butter on crackers (with raisins) for at least one meal a day - sometimes two!
We've tried other things for her lunch over the years, but we found that she was just throwing them in the trash and eating more of the snack that was provided every day instead. NOT a way to raise a child with healthy eating habits. We tried having her eat the school's lunch, but found out the hard way that the school was not/could not handle enforcing the 'meal-only' option, so my kid's lunch purchase record was filled with cookies and ice cream and chips - often several at the same lunch time!
So, for all those holier-than-thou attitudes out there - it is not so easy to just MAKE your kid eat something else, and you cannot just wave a magic wand and 'poof' somehow FIND something they will eat. You can try and try and try and still come up with NOTHING!
Now I have friends who have kids with deathly nut allergies (and egg and others), and I totally feel for the issues they face every SINGLE day in ensuring that their children are in a safe environment. Having said that, a food allergy is not a 'special need' like being deaf or dyslexic or autistic - many of those children ARE put into special classes to work with 'special ed' teachers to help them with their needs - and there is absolutely no reason why the deathly-allergy kids could not have been put in the same classroom. The kids wouldn't have even known about it if the blabbermouth ADULTS didn't make a big deal of it - they certainly don't care. Heck, the parents of the allergic kids might appreciate having other parents in the same class to support each other and know that they can rely on other adults to help keep the classroom allergy free for class parties, etc. The school screwed up in the first place by spreading these children out so much.
Having said all that, this issue goes beyond the child just being hungry because he can't eat his lunch at school anymore - he is actively hating to go to school and I'm sure that that is going to translate into behavior issues in the classroom as well. This IS a situation that requires some kind of intervention, otherwise your friend is going to have a child with very negative issues about going to school for a looooong time. We might expect that in an older child, but that is just a positive tragedy in a child that young!
So, things to do:
--Your friend should have a conversation with her pediatrician. The superintendent is going to appreciate some 'medical advice' from her side of the equation to balance the medical need of the other student. She should have her son evaluated - physically and mentally by the doctor. Is he losing weight, is he showing serious attitudinal differences - is this something apparent to the doctor? If so, and the pediatrician is willing to write a note on her son's behalf that may induce the schools to help provide accommodation for her son.
--She should discuss the negative influence this whole issue is having on her son's ability to learn and contribute to the class - at a minimum because he's too hungry, at a max if he becomes disruptive to the class.
--You don't mention is this is a private or public school, she may have different options if it's public than if it's private. Explore these.
--She should continue to try new/other foods on her son. It's possible that the accommodation that might be reached might not be a pb sandwich, but instead that an aide heats up a kraft macNcheese cup or a chef boyardee pasta bowl or something on occasion. Maybe he can get by with a cheese stick like string mozz or cheddar and some crackers and baby carrots. Odds are that these kids are going to be off and on in his classes for the rest of his school career (barring him or them leaving the school), and she should continue to push the envelope with him, eating-wise. That is the long-term strategy however.
--Looking closely at the setup at the school, what can she suggest as a solution - because going to one of these meetings with only problems and no ideas for solutions is overall a waste of time. So, she should ask them to move the other child, yes, but if they won't, and they do have a valid point, then she should suggest other options. Her child eat somewhere else, possibly (and a hungry five-year old can wolf down a sandwich in 5-10 minutes, easy, so it's not like he would have to be supervised separately for very long.) It might help with the transition for him - he might not prefer that, and be more open to other items to eat if he can stay with the rest of the class. I've found that the most helpful thing is if the child makes the decision by themselves, rather than an adult imposing it on them, they are much more agreeable. The trick, of course, is guiding them to making that decision without it being some kind of punishment.
--She should make sure her child understands about allergies, that some children have them (WITHOUT naming the other child, necessarily), and that they can be very dangerous. IF he is allowed to eat his pb sandwich somewhere else, he needs to practice very strong hygiene habits after he eats it - like using wipes on his hands and face, then additionally washing his hands with soap and water. The reason being that even exposure to the peanut oils that might remain on the mouth, get rubbed onto hands or clothing, and then get transferred to a toy or surface the other child might touch CAN SERIOUSLY INJURE THEM.
At the end of the day, it is true that the risk of death or injury to the other child trumps a hungry and poorly behaved one, but as so many moms on here like to say, your friend is HER child's best advocate and she should continue to try different things to find the best possible solution for ALL parties in this situation.
HTH, good luck!