What might prompt island girl to be extravagant (8)

I believe the answer is:
prodigal
'extravagant' is the definition.
(similar in meaning)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for prodigal that I've seen before include "This son got the fatted calf" , "Extravagant - lavish" , "Improvident" , "Squandering" , "reckless" .)
