This happened to my ds in first grade for the whole school year. Ds is allergic to peanuts, dairy, egg, hazlenuts and a number of of fruits/vegs. He sat with one other student and if that student was absent (bc that student had more medical issues than just PA) then ds was by himself. I tried all year to let them invite someone to the table and the school didn't want that because they were terrified that ds would have a reaction at school.
The saddest part of ds' day was lunch. It was ostracizing and exclusionary for him. It got to the point where he didn't want to go to school because of lunch. (And he's a bright kid who usually likes school, so this was really bad.) They'd do birthdays in the cafeteria (yay for that) but he'd sit there usually by himself and get nothing because no one thought to include him or tell me when the birthday was.
He is VERY social, so this stung. It was safety over inclusion that year and it left a bad taste for both of us with the school because of it. When he started trying to refuse to go to school and fake illnesses because of lunchtime, I knew we had to do something. I didn't want this to permanently tarnish his enthusiasm for school, and it could have if it continued.
We moved the next year to a new district in a different state. The first thing I did was make sure in his 504 that he could sit where ever he wished. I figured where we don't wipe down movie theater seats or restaurant tables, then he could sit in the cafeteria where he wanted to also.
He does have some contact reactions here and there from dairy (and hazlenut coffee randomly), but they are minor and only result in located hives. In his case, the risk at the regular table has been worth the reward for us. Ds has a great group of friends that he's sat with at lunch for years. He's now going into 8th grade and some of the "lunch bunch" friends are boys who he became friends with in his 2nd grade class when they all sat together at lunch back then. He's been sitting with the same core group of boys every year at lunch since I made that change in the cafeteria when we moved here back when he was 8. (He's 13 now.)
There are times where dumb things happen- like milk spills, or someone horsing around with food (middle school hormonal boys) , but they are rare (maybe once every other year) instances and ds advocates for himself with his friends. His friends care about him so usually they are good about the food stuff in the cafeteria.
I'm telling you our story because changing things for ds in the cafeteria in second grade made a huge difference in the quality of his life at school over the years. That's how he found his buddies. At this rate, he's probably going to be sitting with these same boys at lunch until they all leave for college.
I wasn't sure at 8yrs old that ds had all of the skills needed to advocate with his friends, nor did I think that the other 8 year olds could stay out of his space at lunch. The school nurse and lunch ladies were a big help in supporting us with this. He had a set seat at their table at the end and for the first year, no one was allowed to sit next to him if they had peanuts in their lunch. That helped to create the "let's keep ds safe so he can sit with us" atmosphere at the table. The kids didn't mind at all.
When ds was in 3rd grade, there was a bubble of kindy kids w/FA's starting at his school. (Ds is an island for MFA's here in our district- most are younger, so we break in the staff here.) The school nurse decided that everyone needed their own safe space in the cafeteria regardless of their allergen, so the allergic younger students have large laminated placemats with their names on them. There are cleaning procedures for the placemats too. That way the students have their own spaces at either then pn free table or at a regular table depending on the parent preference.
I don't know if any of this would work in your situation, but I wanted to give you something to chew on as she gets older.
Can they put a desk at the end of a regular table just for her so she can sit with the group but have her own safe space? I really feel for you. BTDT and my best advice is to NOT let it go the whole year like this if you can in any way possible.