How to Get the Friends You Want by Peony Pinker

Peony Pinker is not 'cool'. She likes animals and messing about, not
fitness routines and celebrity news. But when Dad becomes a celebrity
agony aunt, the coolest girls in school invite Peony to join their
group. Now she's watching the right films and doing the right
activities to fit in... and she hasn't got time for her old friends any
more. But is the 'cool' crowd really where Peony wants to be? A funny,
thought-provoking story with a subtle self-help theme.