I think that the original source of the Mary Jane Domer as Dewalt’s wife came from "Prominent Iowans" by Brigham. It can be shown that this work contains numerous errors and so I would not give it much credibility. Once some data is published, it is copied by many and appears to be more authentic each time. Speculations seem to become fact after several sequential steps of copying. Unfortunately sources for the data are rarely given.
There were at least three Dewalts/Theobalds who came to America in the same time frame, 1733, 1746 & 1753. It is possible that data was mixed up between these and any one of them could have been married to Mary Jane Domer. The one who came in 1753 was the only one that came with a wife.
I trust the works of Shultz, Jenkins & Gustav Angne more than others because it is apparent that they spent considerable time researching.