One problem with the Susannah Morrison connection is that:
that Elias Lowther is well repreresented in the censuses from 1810 to 1850. If your Elias is one and the same he would have had to have travelled back and forth from IN to VA every decade for the census. This is a conflict w/ your 1840 data for him being in White Co. IN
Perhaps your Elias is the one that married Margaret.... I think if there was some way to confirm your Lowther's wife - the pieces would start to fall into place.
If you have some information that you can share perhaps we can look at this from another perspective. Unfortunately, the Lowther's are not my direct line but they had a profound influence on the dynamics of some of my lines that I cannot understand my line util I understand this Lowther Family.