She uses sterling in a doubtful deal (5)
I believe the answer is:
della
'she' is the definition.
'sterling in a doubtful deal' is the wordplay.
'sterling' becomes 'l'.
'in' is an insertion indicator.
'a doubtful' indicates an anagram.
'deal' with letters rearranged gives 'dela'.
'l' going into 'dela' is 'DELLA'.
'uses' is the link.
(Another definition for della that I've seen is " - - Street (Perry Mason)".)
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