A country girl is able to lead (6)
I believe the answer is:
canada
'a country' is the definition.
(I know that Canada is a country)
'girl is able to lead' is the wordplay.
'girl' becomes 'ada' (girl's name).
'is able' becomes 'can' (if you can do something, you are able to do it).
'to lead' means one lot of letters go next to another.
'ada' after 'can' is 'CANADA'.
(Other definitions for canada that I've seen before include "Weight units" , "Its flag includes the maple leaf" , "Queen Elizabeth is it's head of state" , "North American nation" , "Country to north of USA" .)