Someone who died in infancy is obviously not the person who got married to Willem Jacobus van Zyl.
I found https://www.blignaut.co.za/familychart.php?personID=I10658&tree...
which suggests that the Jacomina Maria Johanna Conradie who married him was born in 1817. Christened: 13 Apr 1817
Daughter of Johannes Hendrik Conradie, Male (1783- ) , c. 25 Dec 1783
(x 3 Apr 1803 ) Cornelia Catharina Jonker, Female (1786- ), born c. 22 Mar 1786, Drakenstein
Married: 31 Mar 1839 Swellendam
Wife of Willem Jacobus van Zyl, Male (1817- ), born b. 22 Sep 1817, Kogmanskloof
In other words a different branch of the Conradie Tree
