They’re wrong to take in the girl (8)
I believe the answer is:
mistakes
'they're wrong' is the definition.
The definition suggests an adverb but the answer is not.
'take in the girl' is the wordplay.
'in the' means one lot of letters goes inside another.
'girl' becomes 'miss' (I've seen this before**).
'take' inserted within 'miss' is 'MISTAKES'.
'to' acts as a link.
Can you help me to learn more?
(Other definitions for mistakes that I've seen before include "Misguided or wrong acts" , "Errors" , "Blunders, slips" .)