Weakness of female, unwell (7)
I believe the answer is:
failing
'weakness' is the definition.
(I've seen this before)
'female unwell' is the wordplay.
'female' becomes 'f' (abbreviation).
'unwell' becomes 'ailing' ('ailing' can be a synonym of 'unwell').
'f'+'ailing'='FAILING'
'of' is the link.
(Other definitions for failing that I've seen before include "Character weakness" , "Weak point" , "becoming frail" , "conking out" , "Defect" .)