Honestly, I think the best thing to do is to ask the teacher why the question was marked wrong. I'd frame it along the lines of "I'm kind of confused because the answer is correct; can you tell me what's wrong?" Something like that. Until you ask the teacher, you're just speculating.
It's true that some teachers can be very rigid. My kids had one of those a couple of years ago, and a long miserable thread was devoted to her on this board.
But at the same time, people also make mistakes, especially if they're grading a lot of papers at once. It's possible that she was looking at the answer to another problem or that she misread the digits your DD wrote. Or whatever. Who knows? Again, if no one asks the teacher, you won't know what's wrong or if it was just an honest mistake. If she was unhappy with something, your DD won't know how to fix the problem in the future. If it was an honest mistake, it's best to find out and move on.
