Setter’s cornered daughter in lane, it’s claimed (9)
I believe the answer is:
allegedly
'it's claimed' is the definition.
(I've seen this before)
'setter's cornered daughter in lane' is the wordplay.
I cannot quite see how this works, but
'daughter' could be 'd' (genealogical abbreviation) and 'd' is found within the answer.
'setter' could be 'gel' (something which sets) and 'gel' is located in the leftover letters.
'lane' could be 'alley' (alley is a kind of lane) and 'alley' is present in the remaining letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for allegedly that I've seen before include "Lay gelled, supposedly" , "By all accounts" , "Conveying something claimed with no proof" .)