Country seat's opening for girl (7)
I believe the answer is:
frances
'girl' is the definition.
'country seat's opening' is the wordplay.
'country' becomes 'France' (France is an example).
'seat's opening' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'france'+'s'='FRANCES'
'for' is the link.
Can you help me to learn more?
(Other definitions for frances that I've seen before include "Name" , "Girl" .)