My G-G-G Lackey was the Lackey (father of Charles, whom you have mentioned) that lived 2 farms away. My records indicate that Charles may have been married twice, the second time in 1881. You state that Mary Jane may have died in child birth.
I would like to suggest an unsubstantiated theory that perhaps Charles and Mary Jane were married and she died as you say in childbirth, Charles remarrying later in life.
As for why she was at her parents during the Census of 1861, if she was expecting a baby, she may have gone to her parents house so that her mother could help with the birth. This was a common practice at that time if your parents lived nearby. Charles might not have been there at the time for various reasons. I know that this was the case in the birth of my own mother 70 some years later.
I also noticed that the 1861 Census form was blank under the headings of married / widowed.