I think it's the teacher imposing a punishment on them that's the problem here. I doubt she would be so anxious if that wasn't a factor. I would speak to the teacher yourself and explain that your dd is getting into a state about the test as she knows she will be punished if she gets a certain amount wrong.
I'm sure the teacher is just wanting to focus them - however, what she is ACTUALLY doing is punishing children for getting spellings wrong; which cannot form part of good teaching for any teacher, anywhere, ever!
i think this needs dealing with - go for it!