2004 Vue 3.5 V6 o2 Sensor Diagram

My wifes 04 3.5 V6 is showing two codes, one being cat malfunction and the other the P0138 o2 sensor malfunction. I'm guessing it's the o2 sensor that's bad and causing the cat code also. It lists Bank 1, Sensor 2. There are 4 sensors on this car, which one is Bank 1 Sensor 2?? I have seen three different diagrams (one from Autozone, two online) and all three are layed out completely different. I'm just going to guess since it's trippng the cat code it's either the one right above it or right below it, leaning towards below, which would be the sensor closest to the muffler (following the flow of exhaust). Am I right, any insight?

Thanks