Question

how do I determine if the o2 sensor is defective (heater element or other) or if it really is sensing "something" that is "really incorrect?"

Answer 1

it is pretty hard to test it without a speacial honda scan tool, usually if there is no wiring issue and no other problems with the car, replacing the oxygen will fix the issue.

also you can check the oxygen sensor relay, there are some Honda's that will need an ECU update to fix the issue.