Thanks.

It's certainly the most likely candidate. However, there is also a christening in October 1819 and one in 1820. The problem is that there is no mention of when any of these children were born. I think that the 1818 date is the date of her christening, though I or the index might be mistaken (I just looked it up on familysearch.org). Another of my ancestors was born in 1818 but not christened until 1824, so it is possible that Mary was born in, say, 1818, but not christened until several years later. Something to check up on, I guess.