Holiday area, one adopted by Rhode Island girl (7)
I believe the answer is:
riviera
'holiday area' is the definition.
(I've seen this before)
'one adopted by rhode island girl' is the wordplay.
'one' becomes 'i' (Roman numeral).
'adopted by' is an insertion indicator (I've seen this in other clues).
'rhode island' becomes 'RI' (US postal abbreviation).
'girl' becomes 'vera' ().
'ri'+'vera'='rivera'
'i' inserted into 'rivera' is 'RIVIERA'.
(Other definitions for riviera that I've seen before include "French/Italian Med. coast" , "holiday destination" , "France/Italy Med coast" , "Warm coastal district" , "Subtropical 1 dn area" .)