Girl getting all upset about nothing (4)
I believe the answer is:
lola
'girl' is the definition.
'all upset about nothing' is the wordplay.
'upset' says the letters should be written backwards.
'about' is an insertion indicator.
'nothing' becomes 'O' (looks like zero - 0).
'all' back-to-front is 'lla'.
'lla' enclosing 'o' is 'LOLA'.
'getting' acts as a link.
(Other definitions for lola that I've seen before include "Whatever -- wants (song); -- Montez, mistress of Ludwig I" , "song by 4 [THE KINKS]" .)