I've just looked at the Preshute marriage and it does say that Charles (or both) was/were from the parish of "Shrivingham". I've also discovered that two of the trees that have this line are from my very distant DNA matches, whom I hadn't made a link to previously.
And, what's even more weird, I looked on FindMyPast for Hedges born in Shrivenham with parents Charles and Mary from 1704 to 1730 and it highlighted that I had already looked up Charles and his daughter Jane (Sarah's sister). Then I remembered, in another branch of the family I have a Jane Hedges b abt 1723 marrying a John Eltham, and Charles and Mary were a possibility for her parents.
If that Jane is Sarah's sister, then Sarah's great granddaughter married Jane's great grandson and the couple became my 2 x great grandparents.