In the previous post (Selway of Somerset - part 1) I pointed to a Find a Grave memorial which says about Mary Selway, daughter of James and Eliza (formerly Maidment): "James and daughter, Mary, went back to England to settle an estate when
James became sick and died in Somersetshire. Mary stayed in England." The source is quoted as "Beaverhead Co. History Book, Vol. II".
Elsewhere (Tribune-Examiner, September 03, 1980, Page 19), the same details and more are found. I read in that Centennial Edition of the newspaper about the children of James and Eliza in Beaverhead County, Montana, "The four boys took up homesteads in the county. [...] The girls married local ranchers except for daughter Mary who remained in England after her father's death and married Tom Porch in Somersetshire. When her two sons, Henry and Tom Porch, were grown they came to Dillon to ranch".
A family memoir available on the internet (by Florence Carter Backus, 1952) says much the same, "James Sr. and daughter Mary (oldest child) returned to England to visit. James died there. Mary stayed there and raised a family."
All these sources, and some others, suggest that Mary Selway returned to England, remained in England, married in England and had children in England.
However, although parish records show that Thomas Porch was baptised in North Wootton, Somerset, England, civil records in the USA show a marriage between Mary Selway and Thomas Porch in Wisconsin, in 1849, a few years after the Selway family emigrated. Then in the same place four children were born to Mary and Thomas Porch.
All things considered, the return trip to England seems not to have been James Selway and an unmarried daughter Mary Selway. It was James Selway, his married daughter Mary Porch plus Mary's husband Thomas and their children. The long journey included three generations of a family across an age range of under 5 years old up to about 75 years old.