Mary's obituary states that she came to Utah in 1850. An obituary for Edward Buys (Mary's brother) states, "With his father's family he crossed the plains in Capt. David Evans' Company of ox teams in 1850."
More research is needed concerning Mary's date of birth as secondary sources and indirect evidence state and imply that she was born sometime between 1834 and 1837. The birth date listed above reflects family tradition (from Family Tree at FamilySearch.org), and data from Mary's obituary.