Hi, Guest123--
I agree with everyone else--hold your head high!!!
I also wanted to give you a little word of encouragement. If this is a public school we're talking about, then you really ARE in the cat-bird seat. How do I know this? Well, for starters, I used to be a public school teacher(I quit to pursue my original profession). I am not one to rattle cages, but there is only one god to which the entire public school dinosaur genuflects(if you guessed money, you're on the right path!), and that god is:
The God of Fear(fear of litigation, to be precise)
I read a quote regarding the food chain as it breaks down in America's public schools, and it went something like this: "Teachers are afraid of principals, who are afraid of superintendents, who are afraid of school boards, who are afraid of parents, who are afraid of children(who are afraid of nobody!)."
Now, I know that's a bit harsh, and a lot of parents and students do not deserve such a bad rap---but you get my drift. Please remember this: Cruella is a public servant---she is there to serve YOU---YOUR tax dollars pay her salary, and she answers to YOU(you do not answer to her). Don't take any of her lip---and if you have even the slightest inkling that she might decide to take her nasty attitude out on your children, you might be so inclined to climb into her face and let her know in no uncertain terms that you are on to her, you're watching her, and that if she so much as breathes on your child, then you'll slap her with a lawsuit so fast that she won't know what hit her. In my experience as a former public school teacher, this is the one thing that principals are terrified of, and in my own experience as someone who has had to stand-up to a bully, you have to strike back HARD.
If you do nothing, then people like this (wrongly)perceive you as being "weak," and an "easy target." It's sick, but what you and I perceive as "being polite" or "being the bigger person" these N's interpret as "shark chum." People like this rarely pick-on someone they suspect would be a formidable opponent. My husband and I just went through this with the N-Neighbors From Hell(they moved, thank God! because we stood-up to them---they probably spent a good 30 years tormenting the other people on our street, and we were the first ones who actually had the gall to put them in their place, but I digress). I rehearsed a "script" over and over in my head, should one of them decide to come outside and engage me in a confrontation(my husband and I waged an aggressive campaign of "ignoring" them while acting absolutely giddy every time we were outside in their presence---N's can't stand to see people happy, and they hate being ignored even more!).
These neighbors had a middle-aged daughter who still lived with them, and she lived to scream at people. Usually her unprovoked outbursts were so abusive that the object of her ire would do everything to just get away from her(..until she made the mistake of picking on me!)

So, one day my husband and I were outside doing yardwork, and this woman came outside for the sole purpose of starting a fight with us. As soon as she opened her mouth, I bellowed out my well-rehearsed, condescending script at her(N's can't stand being patronized!), she retreated to her house, attempting to bark out a comeback but obviously flustered by my unexpected retaliation, and that was the last of it with her(did I tell you that they moved??! I'm sorry, I guess that I can't hear those glorious words enough!)
Was it hard for me to do?! Absolutely! Was my face beet-red, was my heart pounding in my throat, and did my hands shake the entire 30 seconds? Most definitely-- I am not, by nature, a confrontational person. That's why I rehearsed what I did(think of rehearsing your responses as being akin to conducting "fire drills" for your psyche---when you know you might end up being in a threatening situation, it is always good to have created a plan and rehearsed it dozens of times, so that when the adrenaline kicks-in, you have the clarity to override your emotions by going into "autopilot," following your inner "fire drill." In my case, it was a script that I practiced in front of the mirror(so that I could rehearse my body language as well as my words).
The script that I made-up was specific to that situation and those particular people, so I don't think that it would be of much help to you. But my parting words to this woman were, "you know, I really feel sorry for you." Of course that absolutely freaked her out, but I share these words with you, because I believe that, like my XNneighbor, Cruella is really a pitiable person. People who are compelled to behave this way are usually miserable, and I would be surprised if any of them are actually capable of sustaining healthy, loving relationships or friendships.
Sorry for my rant, Guest123--I hope that my meanderings were of some help to bolster your resolve. Stay strong, and keep us posted!!!
PQC