Sadly, we found the AGGS appeal system inadequate, desultory and totally untransparent But we didn't get in, so we would, wouldn't we?!
So sorry to hear your DD did not pass Countrymum.
Having been through the AGGS appeal process and in total agreement with OA about their appeal system I still have no regrets about appealing.
We asked DD if she wanted us to appeal, she said yes so we appealed (making sure that she knew that there was only a very slim chance of a place and that she should concentrate on her allocated school.) Yes it was time consuming and daunting but I can hand on heart say we fought hard for a place for our DD and she appreciated that.
Last year all the appeals granted were for in catchment and qualified but in previous years some appeals were granted to non qualified girls (I think in the seven form entry year groups). You could ask for this info from AGGS but be very specific as to what info you need from them otherwise you will get a generic x number of appeals granted in x years like I did.
If you do decide to go down this route I am happy to PM you any of the info I have that may help.