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