Wol I am thinking of you and your daughter. (((Hugs)))
Here is something I have learnt (on my own, in my denial period). If you want something (and remember you have the right to want something) try to speak face-to-face with the person who has the power to meet your need.
If I read your posts correctly, you want your daughter to stay in a school she loves. The rules say you cannot have this. Here's a little secret, rules can be broken. You pushed at the boundary of the rule by making that phonecall and asking the principal to call you - go you, that was very strong. You didn't get through the boundary, the rule has held firm and you are left hurting.
You are left with a choice, you can let it go or you can have another go at breaking the rule to try to get what you want. Only you will know what is the correct choice for you.
If this were me having a second go at breaking the rule, I would ask for a face-to-face appointment with the principal where I could put my case to him / her. In the meeting I would remember that I have the right to want my daughter to stay in the school where she is happy, this will come across in my body language and in what I say. I would try to be assertive (something I find very difficult), I would try not be passive (something I find very easy), I would not be agressive (I don't know how to be agressive, it was beaten out of me as a very young child).
Fwiw I have worked in a school . Agressive parents never got what they wanted with our head-teacher, she was a tough cookie. The most successful parent I saw getting her own way just never went away but she was always assertive stating what she wanted for her son.
Good luck to you, IWTH xxx