It was a one-page paper that that scored a 92 (B+) with 8 of just this one word marked as needing to be capitalized and no other marks or comments on the paper. So, I'm thinking 8 marks, 8 points off. I actually think it was well-written, with good flow, organization, and content (as much as can be said of a paper that had to be precisely one page!) and no other spelling or grammatical errors.
In the whole scheme of things, I'm not sure a 10yo's paper is ever really all that important. However, she likes to get good grades and she would hate in the end for this paper to make the difference between a B and an A. I've advised her that it is of utmost importance that she is very polite and doesn't come right out and accuse her of being wrong (which I don't think she'd do), but that she can say she was wondering if she could take a look at her paper to talk about it, at which point she could tell her that all the dictionaries she checked told her not to capitalize it. I also reiterated that she is to just drop it if the teacher holds her ground. DD is not the argumentative type, so hopefully it will go smoothly and be a non-issue. The teacher is a really nice person, so hopefully she'll be receptive and my DD will have a posititive self-advocacy experience.
Thanks again, everyone, for your advice!
