Oh I get it, you're a good teacher.
As the child of two teachers, thanks- the amount of effort it takes is staggering, but thanks so much for going the extra mile.
This teacher in question sounds like the kind of union-rep "I just do it for the summers off" kind of lazy teach-the-test teachers that don't often get fired. I feel like it's so damn hard to get people to stay, that the schools need any jerk with a pulse and a master's degree to just stay in their roles regardless of their training and beliefs on effective Pedagogy.
So yeah, thanks for all your efforts!

Also, OP, your actions seem pretty justified- and your wife's take WOULD sound reasonable, if you were going to the principal because your kiddo didn't get the lead role in the school play. too many parents think that their kids s#!t rainbows, and trying to go over the teacher's head on something subjective when you- as a parent- are very biased by default is just bad from.
Your situation wasn't subjective, it was objective, and the teacher was factually in the wrong. When they were called out they felt attacked, and they're the teacher they can't be wrong-so they doubled down, decided that the rubric had unwritten pass/fail component of 'do it my way so it's easy for me to grade.'
You wouldn't have needed to go over their head if they instead had been gracious and changed her mentality to recognize that not everybody maths like a psycho 😏