Female is extremely happy, which is suspicious (5)
I believe the answer is:
fishy
'is suspicious' is the definition.
(synonyms)
'female is extremely happy' is the wordplay.
'female' becomes 'f' (abbreviation).
'extremely' means to remove the middle letters (only the extremes of the word are used).
'happy' with its centre taken out is 'hy'.
'f'+'is'+'hy'='FISHY'
'which' is the link.
(Other definitions for fishy that I've seen before include "Arousing suspicion" , "Questionable" , "Suspect" , "Suspicious, shady" , "Suspicious (as trout?)" .)