Three complaints about your bike?
I would suspect that a clumsy mum caught her ankle on a pedal and laddered her tights, and of course it's all your fault. If that clumsy mum is pally with the head, then I can see how this all came about.
I'd be filled with righteous indignation too, and now that your oppostion is in the open and you've decided to make a crusade of it, good luck to you: you have right on your side. There's no doubt that you're right and she's wrong here.
But I can't help thinking that, at least for you and your child, you'd have done better to quietly continue to disobey. Eventually everyone would have got used to you and your bike, and the head could quietly forget all about it. Other parents might have followed your lead. As it is, she'll lose face by being seen to back down or be forced to back down, and she's already demonstrated that she's not big enough to change her mind (although she's tried to backpedal a bit).
Still, your campaign perhaps has more chance of making things better, officially, for all the other kids in the long run. And it seems you're committed now anyway. Hope this turns out well!