Wrongly infer the daughter is an ally (6)
I believe the answer is:
friend
'an ally' is the definition.
('friend' can be a synonym of 'ally')
'wrongly infer the daughter' is the wordplay.
'wrongly' indicates an anagram (I've seen this in other clues).
'the daughter' becomes 'd'.
'infer' with letters rearranged gives 'frien'.
'frien'+'d'='FRIEND'
'is' is the link.
(Other definitions for friend that I've seen before include "Quaker - pal" , "Pal, amigo" , "One in need is one indeed" , "Organisation's supporter" , "Pal or buddy" .)