T-P, I agree with Amber's sentiments. Two sentences in your post stood out:
I am reasonably laid back about where my DD goes to school.
One of the reasons that we moved to this area was to get her into the comp, I hadn't considered the GS, because I abhor the system.
Your daughter is ten (not yet a lady, although as a father of a 13 year old "lady" I know what you mean,) and you come across as a sensible parent who has thought carefully about her daughter's academic future. You know best and the quotes above show that you considered the schooling circumstances carefully. As far as viewing AHS is concerned, what's done is done and can a 9-year old really
have her heart set on something she knows so little about and could she realistically
(at the age of 9) have judged the comprehensive's lessons as representative of potentially seven years' education at that school, let alone judge that the work she saw was work she did at the age of 6?! There are other avenues for talented musicians if the school does not have an orchestra. Aylesbury Music Centre draws children from a wide radius of schools to its various orchestras (although it comes with the health warning of being on AHS premises...) and I'm sure there must be equivalents in Oxfordshire.
My advice would be that if you intend to appeal, do not tell your daughter. Spend your time and energy ensuring she views the transition to her next school as a positive step and that she gets the most out of the rest of year 6. It would be a great shame if her obvious ability and potential went unfulfilled in this important year because she is dwelling upon what she considers to be failure. If an appeal is successful, you have the luxury of choice. If unsuccessful, your daughter is spared further disappointment.
Go back to those two quotes of yours. You abhor the system and if you really
want to be, you are now free of it! There are many, many parents on here that do not have the positive alternative of an Outstanding comprehensive school where their child has not met the qualifying score so you have already done your daughter a great service by ensuring that she has an Outstanding option irrespective of the selection result.