Demo includes brief audition for leading lady (9)
I believe the answer is:
matriarch
'leading lady' is the definition.
(a matriarch is a woman who leads)
'demo includes brief audition' is the wordplay.
'demo' becomes 'march' (demonstration).
'includes' is an insertion indicator.
'brief' means to remove the last letter (a shorter or briefer version of the word).
'audition' becomes 'trial'.
'trial' with its final letter removed is 'tria'.
'march' going around 'tria' is 'MATRIARCH'.
'for' acts as a link.
(Other definitions for matriarch that I've seen before include "Dominant female" , "Dominating female" , "Powerful older woman" , "Woman dominant" , "Female head of a family or tribe" .)