Thank you for all your replies. I'll try to answer the questions you have raised and apologies for not quoting anyone.
Catchment school: Ofsted report was recent (less than 9 months) and the primary reason for it being downgraded from good to RI was based on a subset of disadvantaged children who failed to make expected progress. Obviously there were other reasons, which include KS4 curriculum not supporting high expectations and aspirations for all pupils, and pupils making significantly less progress in maths across KS3 and KS4, than in English. However, the school appointed a new head with a proven track record at the start of the school year and this report is more likely a reflection of the previous management, rather than the current. DD has visited the school many times - the secondary school maintain excellent links with all the surrounding village schools. Their facilities are good and , whilst I know of parents who have removed their children from the school, I know many parents who are really happy with the school, particularly those with children in the lower years.
Due to the catchment that the secondary serves, it is entirely possible that some of her friends will be 20-30 miles away. Although, I would hope that she will have some friends in the local area too. The school isn't oversubscribed, so transferring there at a later date would be possible.
Advantages: local, shorter travel time, she will know lots of people there and the initial transition will be far smoother.
Disadvantages: results and will it be a good fit for DD?
Grammar school: this is state, not private and is co-ed. Previous years have had a pretty even mix of boys and girls. Results are great, but with it being a selective, it would be a worry if they weren't. All of DD's extra curricular activities are in our nearest city, where the first bus would drop her back off. My parents live in the city and she could easily go to theirs before going to gymnastics and swimming. As luck would have it, both are a 5 minute walk from my parents home. Entrance test is in October; it is a combination of VR, NVR and mathematics. DD was given access to some typical questions during the open day and she breezed through them. Additionally, as she is a late August born, she will have a slight advantage as the results are age adjusted. In all honesty, I wouldn't be in a position to facilitate friendships with her school friends, who could conceivably be anywhere up to 50 miles away. DH's work is based in the town where the grammar school is situated, although he is field based, so only there at the start and end of day.
Advantages: results, extra curricular activities and could it be a better fit for DD?
Disadvantages: distance - I do think it really is a long way to travel at just turned 11, limited opportunities for friendship outside of the school day.
Local School (8 miles away): Moving to be closer really isn't an option. Conceivably, we could appeal for a place - the school has a really excellent gymnastics team which have competed regionally, so we could certainly use that as an angle for any appeal. Due to the buses in our ares, DD would still be leaving home at the same time as she would for the grammar school. However, the school is in the same city as my parents home and she would only be a short bus ride away from them.
Advantages: the school results are better than the catchment school, despite having similar intakes, gymnastics and the fact it would be less journey time than the grammar school.
Disadvantages: there is no chance of DD getting in without appeal and there is no guarantee the appeal would be successful, she will not know anyone going to that school.
To complicate matters, I hope to begin a PhD in the next 6 months; the university is 55 miles away from where we live, but I have made the same commute for the last 4 years during my undergraduate and postgraduate degree. Logistically, DD being in our local school would be beneficial. I cannot base our decision solely on what would be most convenient, though.