I'll have you both know I finished the movie yesterday and enjoyed it for the masterpiece it was. A little research shows that Jill McBane's dramatic character flip was an intentional device written in the script by Leone, and a similar change can be found in Cheyenne. Leone wanted to build his characters up to a point and then quickly reinvent them - almost a fake out. Slightly unconventional, but the impact on the viewer was immense. It's not common I am overcome with malice just by the sight of a character - that's effective movie making.
This movie also demonstrates how heavily Leone's westerns had matured from when he was remaking Yojimbo in A Fistful of Dollars. The Good, The Bad, and The Ugly and Once Upon A Time in the West were, expectedly, triumphs of film.
But my heart still aches for Jill McBane. I don't know why I expected a strong female lead in a Western. That's my own fault more than anything.