When eventually in credit, girl gets squeeze-box (10)
I believe the answer is:
concertina
'squeeze-box' is the definition.
(I've seen this before)
'when eventually in credit girl' is the wordplay.
'when eventually' becomes 'once' (once something has eventually taken place).
'in' means one lot of letters goes inside another.
'credit' becomes 'cr' (abbreviation).
'girl' becomes 'Tina' (girl's name).
'once' placed into 'cr' is 'concer'.
'concer'+'tina'='CONCERTINA'
'gets' is the link.
(Other definitions for concertina that I've seen before include "fold" , "gig belonging to American" , "Musical instrument with bellows" , "Crush" , "Squeeze box" .)