Girl’s advantage going west (5)
I believe the answer is:
tessa
'girl's' is the definition.
'advantage going west' is the wordplay.
'advantage' becomes 'asset' (I've seen this before).
'going west' is a reversal indicator.
'asset' back-to-front is 'TESSA'.
(Other definitions for tessa that I've seen before include "Girl's name; former savings account" , "Woman" , "Dahl or Jowell" , "Girl's name, forerunner of ISA" , "Girl" .)