Greenhalgh

Greenhalgh Manchester sent on 7 years transportation, later married Mary Lenehan. The wall i have hit is that Mary's Death certificate shows her parents as Daid Walsh/Mary Coglan, there was a Mary Lenehan born same area Ireland 1811, and i am wondering if she adopted this name for Criminal issues, otherwise why list her parents as such, they had a child Mary Walsh, same time and place in Ireland.???????