Interesting points to consider:
1. Humidity is where it needs to be (though I may bump it up because she's due for a shed).
2. She's been in this terrarium for nearly five months and is almost always found in the jumble of logs and artificial plants that I have placed on the back of the cool side of the tank (though it runs along for a while to the warmer part of the terrarium). As I indicated in my original post, inasmuch as nothing has changed in her habitat, the temps or the humidity, this behavior is a radical departure from her usual behavior.
3. This is the first that I have heard that too large of a meal can drive a snake into water. I am quite interested in the source of that information. Doubly so, in that she went from a (largish) small rat to a (smallish) medium rat a few days before she began manifesting this unusual behavior.
Peace