Hi Megs mum
Suggest you read through some of the sticky posts first:-
I'm afriad to say that even if your daughter had scored 318 and was on the waiting list there would be little chance of getting a place. Sutton Coldfield Girls made offers to 165 girls, 15 over their PAN and I am aware of at least 6 girls who scored 321 who have not been offered places (due to distance from the school). They have been told there is little chnace of getting a place via the waiting list as the vast majority of offers are accepted.
So if you Appeal it will have to be on the basis that you you have clear evidence of your child's ability from her performance at primary school and that she clearly grossly underperformed on the day of the exam for whatever reason. You would also need to get the fully support of the primary Head in this assessment.
Suggest you read through the posting and in the first instance talk to your primary school head to gauge his/her view.