Elinor Glyn a rather scandalous novelist ; a contemporary verse went 'I'd like to sin/With Elinor Glyn/ Lying on/ A tiger skin''; wrote a novel called 'It' in 1927. In 1928 this was made into a film , starring Clara Bow, a sex symbol of her day. 'It' supposedly meant sex appeal. Clara Bow was billed thereafter as 'The It Girl'. This was all a bit coy. The public would know that 'doing it' and 'to do it' meant sex itself and the heroine was evidently meant to be 'one of those girls who do'. The term has been revived of late. Evidently the Press have taken to calling Lady Victoria Hervey 'an (or the ) It Girl'