Just noted this from earlier:
"Better to ask an evidently very young woman out alone at 4 in the morning more about herself."
She was't alone.
She was with someone who looked and claimed to be 17. (There is no info on how the night panned out for the 13 year old, but there do not seem to be any cases brought, possibly because strict liability no longer applies)
The judge has seen the girl, and CCTV of her that night, and there is evidence from the police, the taxi driver; I do not think that they were all in a conspiracy to leave very young, underage girls out drinking and partying (especially not when in the very patrol charged with stopping that).
It would be wholly exceptional for a 12 year old to convince a police patrol that she was materially older. But that is what is described as happening. And contributed significantly to the sentencing decisions.