If she has that severe of allergies, they only have a TABLE rather than a whole cafeteria policy? It is not uncommon for schools to be "peanut-free" these days with the number of severe allergies out there.
I agree with who said that she needs a friend to sit with! If the cafeteria limits all the "peanut-free" kids to sit at one table, chances are high that she might not know anyone at the table! For a 1st grader, that might be intimidating.
With that said, the tantrums should be on their way out, if they aren't, then you need to try something else. When I had a student that had tantrums, I really just ignored them. Pretty soon they learned they weren't going to get what they wanted from acting that way.
There is going to be little you can do from home to resolve this - the school needs to come up with some strategies. She is still young and waiting until she is home for a reward or consequence for an action that happened hours ago is not realistic. What ideas does the school have??
OR - does she like shots? explain her allergy, and if she doesn't follow the rule then she will have a reaction that she needs a SHOT for.
If she is kicking, biting, and scratching you, that is not acceptable. I would give her the choice to sit at the peanut table with a chosen friend, or she can sit in the office by herself. Tantruming and those behaviors are NOT acceptable and she needs to be taught that. She isn't just going to get over that on her own...