I think this song is retrospective. She is remembering when she was younger and she admired a girl called Sarah because she is indifferent and cool. But now she is older she has realised that it was silly; the lyrics "tarmac of the melting motorway" suggests Sarah has died in an accident and it was because she was too "cool" to care for speed limits, or something. The tone of the chorus suggests she is mocking her former self when she admired Sarah but now realises that her very coolness caused her death.
I think this song is retrospective. She is remembering when she was younger and she admired a girl called Sarah because she is indifferent and cool. But now she is older she has realised that it was silly; the lyrics "tarmac of the melting motorway" suggests Sarah has died in an accident and it was because she was too "cool" to care for speed limits, or something. The tone of the chorus suggests she is mocking her former self when she admired Sarah but now realises that her very coolness caused her death.