Thanks, Adrienne. Nice to hear from you again. I haven't looked at this family for a long time.
I counted 4 younger sibs of Thomas Lace down to a 4-yo so I can't blame Peg Gelling for being reluctant. Her child by Thomas was baptized a little over a year after his father died, so they may have gotten together soon after that event. Both of her parents were alive at the time, her mother Elizabeth (Kelly) dying in 1836, father Thomas of Ballanicholas 1853. I can't speculate why they didn't marry, unless her parents had some issues with Thomas and his family, but she was an adult so could make her own decisions.
The witness to John Lace's 1732 will, Henry Gelling, is likely the one b 1785 German s/o Thomas Gelling & Ann Shimmin. He married a rather elderly spinster Elizabeth Quayle in 1824 Braddan and they lived in Douglas. I don't find any connection to Peg Gelling and her parents.