Ford focus p0420 code. Log uploaded cat or o2 sensor?

Hello, not sure if I am in the right section for this but I don't see anything else. A family member got a p0420 code with their 2013 ford focus se flex fuel. The shops were trying to charge roughly $3,000, $900 for just the catalytic converter part alone. Found the same part for about $200. Anyway, I'm trying to see if it's a o2 sensor or if it's actually the catalytic converter. Car has 115,000 miles so I have my doubts but you never know.
I started the car and logged it for 7.5 min. at idle. The post cat sensor is a narrowband but the pre cat sensor seems to be a wideband, I had to search for the parameter "WB EQ RATIO BANK 1" to finally get reading from it. The first 4-5 min. of idling the voltage from the narrowband is all over the place but once the o2 sensor warms up the reading seem pretty steady, however, towards the end of the log I have some sudden voltage dips, so I'm not sure if this is a sign of a bad o2 sensor or not. Any thoughts?
Attachment 107552

According to this family member, she hasn't noticed any delay in acceleration so I'm not sure if it actually needs to be replaced, looking at repair videos, you have to unbolt the motor mounts and move the engine forward to get enough clearance. This is a little more "involved" than I would like and I'm contemplating if it is the cat, to just tune the car to stop the p0420 code from showing so she can pass emissions in the future and have her fill up with e85 a few times to try and clean up the exhaust system a bit. It's a family owned company car so I think they would prefer to pay $100 vs $2,000 or more for a car they don't really care about much with little value.