Girl taking horse round island (5)
I believe the answer is:
marie
'girl' is the definition.
(girl's name)
'horse round island' is the wordplay.
'horse' becomes 'mare' (mare is a kind of horse).
'round' means one lot of letters goes inside another.
'island' becomes 'i' (geographical abbreviation).
'mare' placed around 'i' is 'MARIE'.
'taking' acts as a link.
(Other definitions for marie that I've seen before include "French queen, d.1793" , "- Lloyd, English music- hall entertainer" , "-- Curie, scientist" , "Queen, guillotined in 1793" , "girl" .)