The girl will shortly account for varnish (7)
I believe the answer is:
shellac
'varnish' is the definition.
(shellac is a kind of varnish)
'the girl will shortly account' is the wordplay.
'the girl will' becomes 'shell'.
'shortly' means to remove the last letter.
'account' becomes 'acc'.
'acc' with its last letter removed is 'ac'.
'shell'+'ac'='SHELLAC'
'for' acts as a link.
(Other definitions for shellac that I've seen before include "Varnish ingredient" , "Resin for varnishing" , "Resin in flakes, used to making varnish" , "Take a shine to" , "old record" .)