Step outside her original story line (6)
I believe the answer is:
thread
'story line' is the definition.
'thread' can be an answer for 'line' (thread is a kind of line). I am unsure of the 'story' bit.
'step outside her original' is the wordplay.
'step' becomes 'tread' (tread is a kind of step).
'outside' means one lot of letters goes inside another.
'original' indicates taking the first letters.
The initial letter of 'her' is 'h'.
'tread' placed around 'h' is 'THREAD'.
Can you help me to learn more?
(Other definitions for thread that I've seen before include "Twine" , "Essential element" , "Prominent spiral part of a screw" , "Line of cotton - plot (of book, film)" , "Dearth of sewing material" .)