Awful article about posh girl (8)
I believe the answer is:
lucretia
'girl' is the definition.
'awful article about posh' is the wordplay.
'awful' indicates anagramming the letters.
'about' means one lot of letters goes inside another.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'article' anagrammed gives 'lcretia'.
'lcretia' going around 'u' is 'LUCRETIA'.
(Other definitions for lucretia that I've seen before include "raped girl" , "Woman in Roman legend" , "The Rape of - (Benjamin Britten)" , "rape victim" .)