Concerned with this lady's adversary turning up (6)
I believe the answer is:
hereof
'concerned with' is the definition.
(I've seen this before)
'lady's adversary turning up' is the wordplay.
'lady' becomes 'her' (her refers to a woman).
'adversary' becomes 'foe' (I've seen this in another clue).
'turning up' says the letters should be written backwards.
'foe' written backwards gives 'eof'.
'her'+'eof'='HEREOF'
'this' acts as a link.
(Other definitions for hereof that I've seen before include "Concerning this" , "Concerned with" , "From this (formally)" , "Of this document" , "Her foe (anag.)" .)