It is purely conjecture that Issabell was a Ginn and that she was the mother of Eliza Jane who lived with John Ginn but the following item supports that view.
On 9/24/1850 the census recorded Essabell Johnson, 40, as head of the house in Moultrie Co, IL . Her children were Eliza, 16, John, 13, Jane, 11, and Charles, 11, all born in Ireland. Down the road was John Johnson, 60, and family, with the same names plus Ginn names, all born in Ireland. Next door to John was Thomas Purvis.
Either Isabell died or remarried and the family split up as no further records have been found.