Jane wonders aloud if Lassiter was Milly's husband. Why would this be important? Would this mean that Lassiter was a Mormon?

Jane sometimes believed that Milly was run off from her home. If Lassiter was Milly's husband and has come looking for her, it might mean that Milly left of her own will. Milly taught in a Mormon school, but it is never said that she was Mormon herself, and, either way, it would not indicate the religion of her husband.