Scots girl fool caught in fib (6)
I believe the answer is:
lassie
'scots girl' is the definition.
(I've seen this before)
'fool caught in fib' is the wordplay.
'fool' becomes 'ass' (both can mean a stupid person).
'caught in' indicates putting letters inside.
'fib' becomes 'lie' (I've seen this before).
'ass' put into 'lie' is 'LASSIE'.
(Other definitions for lassie that I've seen before include "''Will ye go ..., go'' (folksong)" , "TV/film dog" , "girl found" , "Screen canine" , "Canine film star" .)