Help musician losing her head (6)
I believe the answer is:
assist
'help' is the definition.
(assisting is a kind of helping)
'musician losing her head' is the wordplay.
'musician' becomes 'bassist' (I've seen this before).
'losing her head' means to remove the first letter.
'bassist' with its initial letter taken off is 'ASSIST'.
(Other definitions for assist that I've seen before include "Work with N help" , "Give a hand to" , "Work as a subordinate" , "Understand by instinct" , "Be useful to" .)