Young lady convict knocked up (3)
I believe the answer is:
gal
'young lady' is the definition.
(I know that gal is a type of young lady)
'convict knocked up' is the wordplay.
'convict' becomes 'lag' (slang term for a prisoner).
'knocked up' says the letters should be written backwards.
'lag' back-to-front is 'GAL'.
(Other definitions for gal that I've seen before include "An American girl, cowboy vintage" , "Broad" , "Girl from American west" , "female noted in Kalamazoo" , "Young woman (colloq.)" .)