I have not come accross the Nelly Girtie name.I would assume since she was from Campbell (Illinois Dist?) that she was married to a close relative of Simon Girty who also lived in Campbell.That line is a bit sketchy.The earliest Girtys from that area were an Isaac and Simon Girty (b. 1780s or 90s) who came from Arkansas Territory.Then theres a gap when Simon Girty (b.1829) appears.Simon's descendants are known, but his connection to the Simon Sr. or Isaac Girty is not completely established. She could have been married to a younger brother of Simon, but I can find nothing on any siblings of his.
There may be other Cheorkee enrollment files available that list Nelly Elliott Girty, but I'm not sure where they would be.