Hi wickerman,
I read this thread yesterday and have been thinking about your daughter, so I thought I'd come back to it.
She sounds like a lovely girl and you a very caring mum.
I don't have experience of this from a parental point of view, but can remember the feeling of being a child when all the girls started pairing off into cliques. I was, on the face of it, a pretty normal child - although my parents were pretty hippyish, so were other people's, so this wasn't too big a deal. However, I still had those moments (still do, sometimes) of thinking I wasn't like everyone else. Like you say, girls of this age are desperate to sound grown up and if we were to listen to their conversations, in which 90% of the group will be faking maturity, it would probably be laughable - but to your DD it might feel like a big secret she doesn't get.
I think there are two things you can do to help.
One is, like others have said, to emphasise that it's ok to be yourself and not conform. There are loads of good role models in books and films, from Maggie in the Mill on the Floss (probably a bit too old for her) to Pippi Longstocking to Lindsay Lohan in Mean Girls!
The other is, that there is some responsibility on you to show her that you can be quite unlike someone, yet still be good friends. You seem to have fallen into a trap of imagining all your neighbours as one homogenous mass, rather than individual people. They may appear to have opposing values, but scratch the surface and you'll no doubt find a group of parents who are as concerned about and in love with their children as you are - even if you have nothing else in common, this is a decent starting point. Some of my best friends are nothing like me. In fact, I think it is easier this way. There is no competition or envy in our relationship, because we are not even aiming in the same direction. I also find it interesting talking to people whose points of view are so different from mine. Others of my friends are actually quite like me, but I'd never have thought it from the way they dress, the jobs they do, the homes they live in etc. There are two elements here - to teach your daughter that each of those girls in her class is unique - they don't all think and feel alike, even if they claim to in order to fit it.
The other is that, to paraphrase High Fidelity, 'it's not what you like, but what you're like'. I think you can best demonstrate this by making some effort yourself to intigrate with other parents from the school/ on your street. It would be great for her to see that, without giving up anything of yourself, you can also get on with others who are so different to you. While the arty hippy commune holiday sounds like great fun, if you have time left, why not spend some time in the holidays in the local area? Perhaps you and DD could take a short course in something you're interested in together and try and meet some other families who live locally.
Sorry that was LONG!