Outstanding Conservative girl in charge (7)
I believe the answer is:
classic
'outstanding' is the definition.
(thesaurus)
'conservative girl in charge' is the wordplay.
'conservative' becomes 'C' (abbreviation commonly used in UK politics).
'girl' becomes 'lass' (lass is a kind of girl).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'c'+'lass'+'ic'='CLASSIC'
(Other definitions for classic that I've seen before include "Of the highest order - the Derby, for example" , "Race, eg Derby" , "Eg, screw thread" , "Of recognized excellence" , "Quintessential" .)