Sally’s type, extremely imaginative (6)
I believe the answer is:
sortie
'sally's' is the definition.
(synonyms)
'type extremely imaginative' is the wordplay.
'type' becomes 'sort' (both can mean a kind or variety).
'extremely' suggests removing the centre (only the extremes of the word are used).
'imaginative' with its centre removed is 'ie'.
'sort'+'ie'='SORTIE'
(Other definitions for sortie that I've seen before include "Military aircraft's flight" , "Military aircraft flight" , "Sally" , "Breakout by besieged garrison" , "Short foray" .)