Old lady rules one African nation (6)
I believe the answer is:
malawi
'african nation' is the definition.
(country in Africa)
'old lady rules one' is the wordplay.
'old lady' becomes 'ma' (both can mean mother).
'rules' becomes 'law' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'ma'+'law'+'i'='MALAWI'
(Other definitions for malawi that I've seen before include "African country, capital Lilongwe" , "Landlocked African country" , "A law I'm making up in Southern Africa" , "Landlocked country of south central Africa" , "Landlocked African state" .)