One assuming female is incapable (5)
I believe the answer is:
unfit
'incapable' is the definition.
(thesaurus)
'one assuming female' is the wordplay.
'one' becomes 'un' (I've seen this in other clues).
'assuming' is a charade indicator (letters next to each other).
'female' becomes 'fit' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'un'+'fit'='UNFIT'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for unfit that I've seen before include "Not in good physical condition, or not suitable" , "In poor condition" , "Ill - out of shape" , "Ill-equipped" , "In bad physical condition" .)