Thanks to those who pointed out that my lack of the word "the" was not a mistake but only me trying to keep the post brief! I was worried, when told had made errors that I could no longer see my mistakes!
For those who say I am in no position to judge the quality of work, I do actually have a degree in English from one of the UK's top universities so I think I can probably make some assessment. However, as I said, am not a teacher so can't claim to know marking scheme.
I understand that DC may not have performed on the day and would accept that if the feedback had been along the lines of "multiple spelling mistakes; lack of advanced vocab used or serious grammatical errors". None of these were mentioned. The feedback was purely stylistic and thus, to my opinion, very subjective. The school, however, will not let me see the work (this is their policy - not sure if that is common across all schools).
I am not confident that the work has been reviewed properly by another teacher. The school will be happy with the grade given as it is within one grade of target so I believe, if any review took place, it was only a cursory glance.
My DC is not a complainer and accepts feedback when needed. It is so unusual to get such a strong response and belief that this mark is unfair, hence why I want to support.
However, am now deeply frustrated that there seems to be no line of appeal and we just seem to be told to put up or shut up.
If anyone has advice or ideas on how I can progress this, would be so grateful.