What I would want in a plan at this school is that your children only eat what you send or what you've approved. Period.
One of our members here, ajasfolks2, has created some excellent wording about that, but I can't find it.
About your situation, wow. I don't know what to recommend for a private religious school. Others here have had that experience. I know of one here who removed her kids from their private Catholic school, homeschooled for a while, and now her oldest can go to a Catholic high school that is different than where he went before. It has really worked out for them.
If your school doesn't shape up and get it, it may be less traumatic for your kids to switch (or at least your FA child to switch) than to remain. Ultimately it's about safety, but inclusion is a goal. This school, unless it receives federal funds, doesn't have to do what it takes to ensure your child's safety OR inclusion. A public school does. Some private schools do great jobs with it.
But if this school isn't even trying, it can mean far worse social consequences than changing schools. And of course, it can have other tragic consequences.
FWIW, my 16 year old son changed schools:
after K
after 3rd
after 8th
All during the summer. Each time to a different community or state.
He is a happy, well-adjusted kid. The last move was the absolute best. He has great friends. When we drop him off, it's not uncommon to hear other kids yell, "Hey <DS name!>" And this is a large high school. Three of his teachers last year at conferences said it's like he grew up here. he has made so many friends, found his niches, and is embracing life at his school.
So--changing schools is not the end of the world. If things deteriorate further socially at school, it could be worse for her to stay.
I'm really sorry you're in this situation. ((hugs))
And I'm glad you found us.