Thank you Frances. This confirms the surname as CORRIN, not CORRIS. Now I can find several children on the IGI and they start earlier than I expected. Also, the Marown marriage is in the notebook for 9 Feb 1754, which also is earlier than I expected.

So Ann Gelling clearly was born prior to the first identified child of John Gelling & Ann Fayle, which is Margaret 24 Mar 1736/37 Marown, followed by a second Margaret 30 Sep 1739.

Ann's sister Catharine (who married William Cubbon ca 1763) and who's been a subject of discussion on this thread, was apparently 70 on the burial index and 71 on the MI for 11 May 1811, which works back to about 1740.
JG & Ann Faile had a John in 1741, a William in 1743, Patrick 1746, Jane 1747 and a late Robert 1753. So there's no room to fit a Catharine in here. Perhaps she was a tad older and is, like Ann, missing? Or one of the Margarets is her. The 6 Dec 1763 marriage of Wm Cubbon & Margaret Gelling sure sounds like it should be Catherine.

I could probably figure this out, but are the baptisms of the early to mid 1730s in Marown missing?

I suspect the parents John Gelling and Ann Fayle married just ahead of the beginning of Frances's Marown list, that starts July 1733. "Them's the breaks" I guess.