At first, nobody usually notices she might have a habit (3)
I believe the answer is:
nun
'she might have a habit' is the definition.
(nuns wear habits)
'at first nobody usually notices' is the wordplay.
'at first' says to take the initial letters.
The first letters of 'nobody usually notices' is 'NUN'.
(Other definitions for nun that I've seen before include "Holy sister" , "Woman in religious community" , "A palindromic lady in religious order" , "A palindromic holy woman" , "Black and white pigeon" .)