Girl has only to aim (4)
I believe the answer is:
goal
'to aim' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for goal that I've seen before include "End" , "Ambition for a score" , "Aim or purpose" , "Aim and objective" , "Objective or score" .)