I think Frances has made a typo re the date of birth of Mark Christian. IGI has christening at Kirk Bride on 8 Mar 1817 s/o Thos. Christian and Margt Cormode. [not 1814]

We might then guess that his wife, in due course, would be a couple of years younger than him, so perhaps Betsy (a pet form of Elizabeth) was born c1819 perhaps??

A good match is an "Elizabeth Tear" who, was conviently, also christened at Kirk Bride in January 1818. But this is of course pure guesswork...