Hi James
I did some checking on my background notes regarding the marriage of Christopher Lethbridge of Westaway, the son of Christopher Lethbridge of Westaway. I have details of a marriage contract between Christopher, the son, and Mary Periam, eldest daughter of John Periam of Milverton, dec'd and his widow, Sarah. On 3rd October 1716, Christopher the father provided various lands in trust to the couple, whilst Sarah provided £2,500 as Mary's portion.
I believe that Elizabeth Cannon Lethbridge was the daughter of Christopher and this Mary.
While I haven't researched it as yet, I think that the later marriage to Mary Dyke would be a second marriage for Christopher. Mary Dyke was shown as a widow, so that would fit.
The Dyke family were an important local family based at Tetton, so Mary as a widow would have been an appropriate spouse for Christopher. Incidentally, the Dykes married into the Acland family, who were mentioned earlier.
I hope that helps.
best regards
David