Hi Aaron. I had another look at the certificate and did some more searching. With a little inspiration, I think I have cracked the mystery but it has created another one.
The first thing I did was search for a marriage between Andrew Forsyth and Jane? in Scotland. This lead to a record of the children born to Andrew and Jean Mowbray( my other guesses for her name were Marbary or Mowbrary)- no marriage. The children were Jane(1815), David(1820) and James(1825). The children were all born in Duddingston, Edinburgh. However, no Christina.
My brother had a similar problem with a name. The relative in question was sometimes recorded as Christina, sometimes as Christian. On the 1861 census, the name looks like Christian. The IGI index did find a Christian Forsyth born in 1829 to Andrew Forsyth and Jean McKenzie(Jean is a form of Jane) in exactly the same place. There was also a son, Alexander Napier Forsyth born in 1822.
So, either there were 2 Andrew Forsyths living in Duddingston at the same time or it's the same man- 2 women. Either scenario is plausible but that doesn't explain why Christian/Christina's mother's name is Jean Mowbray unless Christina was brought up by her.
I don't know if this matches up with anything you have......
Karen.