Mum’s right to follow friend (5)
I believe the answer is:
mater
'mum's' is the definition.
('mater' can be a synonym of 'mum')
'right to follow friend' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to follow' is a charade indicator (letters next to each other).
'friend' becomes 'mate' (mate is a kind of friend**).
'r' put after 'mate' is 'MATER'.
(Other definitions for mater that I've seen before include "parent" , "The alma . . . . . Is the old school (5)" , "See 12" , "Mother (sl.)" , "mum's the word" .)