Young lady gets three keys (3)
I believe the answer is:
deb
'young lady' is the definition.
(short for debutante)
'three keys' is the wordplay.
'three keys' means three substitutions for 'key'.
'key' becomes 'd' (musical key).
'key' becomes 'E' (musical key).
'key' becomes 'b' (eg B major, musical key).
'd'+'e'+'b'='DEB'
'gets' is the link.
(Other definitions for deb that I've seen before include "Young socialite" , "One coming out" , "Girl just entering society" , "In brief, a society girl getting out of bed" , "Young woman coming out in society, in short" .)