How does Barbara come to be a part of Jefferson's life in the novel, The Winning of Barbara Worth?

Years before the novel's start, Jefferson Worth's outfit was delayed by a three day sandstorm in the desert. When it was over, the men discovered a dead bay horse along the trail, and a bit further at a dry water hole, a dead woman and a little girl of about three years old who called herself Barba. Jefferson Worth raised her as his own