A posh girl takes it in charge (5)
I believe the answer is:
debit
'charge' is the definition.
(debit is a kind of charge)
'a posh girl takes it' is the wordplay.
'a posh girl' becomes 'deb' (short for debutante).
'takes' means one lot of letters go next to another.
'deb'+'it'='DEBIT'
'in' is the link.
(Other definitions for debit that I've seen before include "Payment made or owed" , "Enter in accounts as sum owed" , "It's not to one's credit" , "Negative entry in the accounts" , "Sum removed from a bank account" .)