African girl keeping a diary up (7)
I believe the answer is:
angolan
'african' is the definition.
(Angolan is an example)
'girl keeping a diary up' is the wordplay.
'girl' becomes 'nana' ().
'keeping' indicates putting letters inside.
'a diary' becomes 'log' (log can mean a record or diary).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'nana' placed around 'log' is 'nalogna'.
'nalogna' backwards is 'ANGOLAN'.
(Other definitions for angolan that I've seen before include "Eg, native of Luanda" , "Coming from a southwest African country" , "One from Luanda" , "from Africa" .)