Small female with delicate retro clothing's a little cold (7)
I believe the answer is:
sniffle
'a little cold' is the definition.
(I've seen this before)
'small female with delicate retro clothing's' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'female' becomes 'f' (abbreviation).
'with delicate' becomes 'elfin' (I've seen this before. I am not sure about the 'with' bit.**).
'retro' says the letters should be written in reverse (retro is Latin for 'backwards').
'clothing' indicates putting letters inside.
'elfin' reversed gives 'nifle'.
'f' placed into 'nifle' is 'niffle'.
's'+'niffle'='SNIFFLE'
(Other definitions for sniffle that I've seen before include "Sign of a cold?" , "A little cold" , "Breathe in, as when having a cold" , "Mild cold" , "Slight head cold" .)