Friend’s after short string instrument and wind instrument (9)
I believe the answer is:
harmonica
'wind instrument' is the definition.
(harmonica is a kind of wind instrument)
'friend's after short' is the wordplay.
'friend's' becomes 'harmonic' (I can't explain this - if you can you should give a lot more credence to this answer).
'short' says to take the initial letters.
The initial letter of 'after' is 'a'.
'harmonic'+'a'='HARMONICA'
'string instrument and' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for harmonica that I've seen before include "Harp" , "Blow me!" , "glasses of water" , "An alternative mouth-organ" , "It's blown" .)