This girl sound in the pink (5)
I believe the answer is:
rosie
'this girl' is the definition.
(girl's name)
'sound in the pink' is the wordplay.
'sound' becomes 'i' (I am not sure about this - if you are sure you should believe this answer much more).
'in the' indicates putting letters inside.
'pink' becomes 'rose' (colour).
'i' put inside 'rose' is 'ROSIE'.
Can you help me to learn more?
(Other definitions for rosie that I've seen before include "Cider with --, novel" , "Cider with - (Laurie Lee)" , "Female" , "riveting woman in 40s?" , "cider drinker sounds red" .)