Her husband, Matthew Chesher, 44, was the chief of staff to roads minister David Borger when allegedly he bought an ecstasy tablet from another man in Sydney's inner-west last Friday evening.
Mr Chesher resigned from his job on Saturday.
Speaking publicly on Thursday after three days of annual leave, Ms Firth said she was 'completely shocked', and described her husband's arrest as 'traumatic'.
'Friday night was probably the worst night of my life. It was the worst night of my life,' she told reporters in Sydney on Thursday.
'I had no reason to suspect him of anything out of the ordinary. I am like a normal wife. I was just at home getting on with the evening."
