Girl touring island, an American state (9)
I believe the answer is:
Here is my best explanation:
'american state' is the definition.
(Louisiana is an example)
'girl touring island an' is the subsidiary indication.
'girl' becomes 'louisa' (**).
'touring' indicates putting letters inside.
'island' becomes 'i'.
'louisa' placed around 'ian' is 'louisiana'.
(Other definitions for louisiana that I've seen before include "Southern US state", "American state, capital Baton Rouge", "Southern United State on the Gulf of Mexico", "State named for French king", "IOU a snail over in the US state", "State of southern US", "US state, capital Baton Rouge" and "US southern state".)