Eric...I am so sorry for your loss.
I thank you for doing the "permie thing" and not killing the snake, and choosing rather to relocate. This is good as long as it is in a safe location for the snake and fare from other livestock that could fall victim to it (unless you would like to kill it and eat it and make things from its skin and bones...I am o.k. with that too.)
If the duck was on a nest...or feeling "grumpy" it may well have "nipped" the snake...Which was the duck's down fall as a 6' Elapid of several species in more than capable of killing most poultry. Seldon (ever?) would a snake even of this size try to
feed on such a large prey item...but will...if provoked kill one. They (snakes) are typically there for rodents and smaller game, though they will take young of the all poultry.
Again...sorry for your loss...and thank you for your wisdom and courage to move passed the anger and accept the balance of things....