Unfortunately, woman prematurely cancelled bill in bank (11)

'unfortunately' is the definition.
(synonyms)

'cancelled bill in bank' is the wordplay.
'cancelled' becomes 'gret' (I am not sure about this - if you are sure you should believe this answer much more).
'bill' becomes 'tab' (tab is a kind of bill).
'in' is an insertion indicator.
'bank' becomes 'rely' (to bank on is to rely on).
'gret'+'tab'='grettab'
'grettab' going within 'rely' is 'REGRETTABLY'.

'woman prematurely' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.