Charged a posh girl for a fancy diet (7)
I believe the answer is:
debited
'charged' is the definition.
(I've seen this in another clue)
'a posh girl for a fancy diet' is the wordplay.
'a posh girl' becomes 'deb' (short for debutante).
'for' says to put letters next to each other.
'a fancy' is an anagram indicator.
'diet' is an anagram of 'ited'.
'deb'+'ited'='DEBITED'
(Other definitions for debited that I've seen before include "Deducted" , "recorded in account" , "Taken from an account" .)