I don't think you really understand the extent of the problem. Nobody is discriminating against your child. Have you ever smelled a peanut butter sandwich when you walked into a room? That peanutty aroma also contains microscopic oil particles that are DEADLY to someone with a peanut allergy. That is why peanuts are no longer served on airplanes.
Add to the problem that small children have at luch when they "share" with their friends, or eat sloppy and have traces of their sandwich on their faces and hands after lunch that can be transferred to another person or a common surface.
It didn't make sense to me either, until my son exlained it to me. Then I was happy to co-operate.
Concerning your child: you are doing her no favors if you don't introduce a wide range of foods to her. I know. I was a picky eater too. When I got to college I quickly learned that I had to eat what was served or 1) starve, or 2) used hard earned cash to get something else!
I raised 4 kids myself and I know that they can be difficult, but we had one rule (even for the picky ones): eat what is served, or go without.
The only concession we made was to leave the mustard OFF sandwiches for one of them. They all grew up great, are considerate of others, finished college with higher degrees, married good folks, gave us terrific grandchildren, and still love us!
There are other sources of protein besides peanut butter. And you child is still able to enjoy PB before and after school. Better a little sacrifice than being responsible for a classmate's death, or hospitalization.
Think of PB asif it were a gun in the case of an allergic child. Would you think that it was too restrictive if your child was prevented from bringing a loaded pistol to class? (Even if there was no intention to use it.) It's really the same thing.