My daughter is similar, so it's reassuring to see all these positive replies. I supect that there are times when I worry too much (perhaps you are the same, dancegirl?), so it's good to see others viewing this type of behaviour as just another way of growing up.
At this age I think some girls are much more into arranging a social life than others. If your dd has good friendships at school then i would not worry - or even if she doesn't, but is 'getting there'. It can be heart panging to see your dd not being part of the groups of girls going round chatting merrily to each other and being arm in arm at these events, but if dd has a couple of friends then that is really all she needs. Would you think it worth having a quiet word with the form teacher or HoY to see if she does have some pally types at school? If so, you can relax - if not, well that's the next stage...
I'm sure I'm probably worrying over nothing but dd1 doesn't seem to have a very good social life compared to her peers. She's in Year 7 at a girls' school and seems v happy, has settled in well and talks about friends. I've said she can invite friends over whenever she likes or she makes some arrangements to see friends etc but it hardly ever happens and she seems happy just hanging around with us at home.
Today was her school Christmas fair. There seemed to be loads of Year 7s all going around together and I asked dd if she wanted to see her friends. She texted one girl but she didn't reply. Dd is quite shy and I wondered if she did want to go round with the other girls but maybe didn't know how to break in. In the end she just wandered around with me, dh and dd3 and we went home after an hour or so. Dd seemed happy enough but I'm worrying that it's bothering her and won't admit it.