Upset old lady penning article is creating disbelief (7)
I believe the answer is:
atheism
'disbelief' is the definition.
(I've seen this before)
'upset old lady penning article is' is the wordplay.
'upset' says the letters should be written in reverse.
'old lady' becomes 'ma' (both can informally mean mother).
'penning' indicates putting letters inside.
'article' becomes 'the' (the definite article in English).
'ma' reversed gives 'am'.
'the'+'is'='theis'
'am' placed around 'theis' is 'ATHEISM'.
'creating' acts as a link.
(Other definitions for atheism that I've seen before include "Lack of belief in the existence of God" , "A lack of faith" , "Owed" , "Sceptic's position" , "displaying opposition to religion" .)