Hi, Frances. Following the suggestion you made regarding whether Jane moved to live with one of her children post-1861, I have now looked at all censuses I could find (Eng and Manx) associated with the children (male and female) of Wm and Jane and did not find her with any of them, so for now, my trail has gone cold.
I still have that 1881 census showing a Jane, age 80, living on Mill St. in Castletown with a brother Thomas, but don't think that's the same Jane, because of the calculated birth year (1801 vs 1798) and that I can't find a brother Thomas associated with the Jane that married William Christian.
We leave for our cruise today (visiting IOM Tuesday 27 Jun) so I won't be following this thread again until I return home. Thank you again for all your help.