Innocent spouse tax relief?

For a couple that was never married but lived together in PA for over 7 years....they filed jointly for one of those years. He was a sub-contractor and never paid his tax debt. She was a homemaker and unaware of any of this. Can she file the innocent spouse tax relief form. If so, on the form, you are asked to check a box for married but legally separated, legally divorced, etc. It also requires you to attach doentation. What does she do if she was never legally married?