Guest, popular girl, needing support on course (7)
I believe the answer is:
invitee
'guest' is the definition.
(synonyms)
'popular girl needing support on course' is the wordplay.
'popular' becomes 'in'.
'girl' becomes 'vi' (short for Violet).
'needing' is a charade indicator (letters next to each other).
'support on course' becomes 'tee' (golf tee on a golf course).
'in'+'vi'+'tee'='INVITEE'
(Other definitions for invitee that I've seen before include "One asked to attend" , "visitor?" , "special guest" .)