One thing I would say about moving to any school is that they will take children in from a number of schools so your daughter may not come across the children she knew at her old school especially if the school is large like you say. She will also be setted according to her ability, so if she is bright chances are she'll be in set 1 (possibly 2) along with other children of her own ability who she can form friendships with. Obviously sport is a consideration for you and her. If she is likely to miss about on anything she particularly enjoys, it might be possible to enroll her in a local club - again this is somewhere she might meet like minded children. It's worth asking about sports club within the schools.
My daughter is in Year 7 and lucky to have children in her tutor group who she really likes (at comprehensive school), but this last week it looks like other friendships are forming, she's been invited to a party and someone else's house for tea. If your daughter can get past the first few weeks, then friendships should start to form and you can always invite some of the girls for tea which I do think helps.
You have a little while to work out what feels right. Obviously do go to the schools open evenings and take your daughter so she can get a feel for both schools. A lot of schools in our area allow you to go back in after open evenings to see the school while children are in lessons, so again this is something you could take your daughter to and it may help get a stronger feel one way or the other.
I had one in private, others in state, right choice at the time. All in state now, might change in future. We shall see.
I understand your anxieties, I changed DS to private for 2 years for similar reasons. The problem wasn't state vs. private pupils, more like that particular set of kids at our local primary. We still avoid the local state secondary just to avoid some of the peer group who were so horrid to DS. I don't think they are (all) horrid kids, but DS might slot back into a certain social place in their minds, we don't want to risk it.
Why not give the comp a try and switch her later if you felt you had to? She is maturing and changing, she can handle different things than she could before. There will be lots of new children she hasn't met yet, in her y7 intake. Her chances of finding like-finder mates are much higher than in y3.
How limited are the sports facilities at the part-selective comp? DD looked at a GDST school that had one small measly playing field (65 x 30m?), she's a strong cross-country runner. . Also a decent swimming pool and a usual-size well-maintained indoor hall. Most the local comps have similar size facilities but for more pupils. Still the small field made me laugh.
that's one of the things I'm mulling over! ds has SEN so none of the local private schools would have been appropriate for him and despite its faults the local school is the best 'fit' for him (in as much as a school-hating boy can think that any school is the best ...) plus all his friends from primary went there which made the transition process a lot easier
however dd doesn't have any friends from the state primary which is one of the feeders and she'd be back with all the children she didn't have anything in common with 3 years ago
She's so happy at her current school (and it's made us realise quite how unhappy she was at her previous school - she is a transformed child) that I'm really anxious about plunging her into a difficult (for her) environment again
Would appreciate some opinions as we may well have a choice dilemma for dd in a year or so
Dd is currently in a lovely private primary - she's been there since the start of Y3 after we moved her from our local state primary where she was deeply but quietly unhappy
She's very bright - finds primary maths and English a breeze and is easily top of her class (school is non-selective) - but also works hard and is conscientious and well-behaved. She's very sporty as well and loves art and DT. She's got a good, small group of friends but is quite shy and reserved and her current head thinks she would be happiest in an all-girls environment
She has a guaranteed place at our local highly-regarded partially selective comprehensive where her brother goes, but .... I'm by no means convinced that she'll be happy there. It's enormous and the pastoral care is not great. The results for the top set children are great and the art is good but there's very little sport (very few facilities). I've seen a GDST school which I suspect would be perfect for her, but of course it's not free!
So, do we send her to the local comprehensive, watch out for signs of unhappiness and then do something or suck up paying fees for another 7 years? Options are going round and round in my head ....