I agree with the comments that identify this young man as controlling. I'd have been as dismayed as you. I'd have offered anything else I could then cook so she could join the other guests but with a controller, even that may not have been enough. My practice when inviting people to dinner is to offer a menu prior and ask if there is anything that would cause problems. I know that allergies can be life-threatening and health conditions can be invisible to others. In any case, I am sorry you had such problems. What a sad end to something that was planned to be so lovely.