Woman a Gershwin musical initially upset (5)
I believe the answer is:
maria
'woman' is the definition.
'a gershwin musical initially upset' is the wordplay.
'gershwin' becomes 'ira' (ira gershwin is george gershwin's brother).
'initially' says to take the initial letters.
'upset' says the letters should be written backwards.
The first letter of 'musical' is 'm'.
'a'+'ira'+'m'='airam'
'airam' in reverse letter order is 'MARIA'.
(Other definitions for maria that I've seen before include "Girl's name; darker moon areas" , "More than one plain" , "musical" , "West Side Story girl" , "Plains on the moon; girl's name" .)