Little Dolores, all upset about nothing (4)
I believe the answer is:
lola
'little dolores' is the definition.
The definition suggests a singular noun which matches the answer.
'all upset about nothing' is the wordplay.
'upset' says the letters should be written backwards.
'about' means one lot of letters goes inside another.
'nothing' becomes 'O' (looks like zero - 0).
'all' backwards is 'lla'.
'lla' placed around 'o' is 'LOLA'.
Can you help me to learn more?
(Other definitions for lola that I've seen before include "Whatever -- wants (song); -- Montez, mistress of Ludwig I" , "song by 4 [THE KINKS]" .)