I think we blew a head gasket - help!

I haven't found much if anything on the 1NZ-Fe engine and the Prius C, so I apologize if this is rehashing an issue. And, I'm new to the forums, although I've browsed them for years when I've needed help. TIA for reading this mess.

The tldr is that I think a head gasket has blown on my GF's 2013 77k miles Prius C Four (probably Three but she's not sure). We're in Northern MI which has been incredibly cold, 0 - -10F when this occurred. It has the classic symptoms:
-rough start and idle,
-creamy coffee colored oil (and ice from the cold+moisture under the cap)
-coolant doesn't appear to be fouled.
-Plugs are oily and fouled, moderate arc scorches around the bottom of the ceramic except for the driver's side cylinder which was better. The center-drivers cylinder had some metal burrs on it.
-The center/pass side cylinder appears scorched when looking down through the spark plug hole and has what looks like black goo in it. The other 3 look OK.
-running with the oil cap off produced a ton of sound and extreme pulsating - no oil visible under the cap when running.
-Compression on the pass side cylinder is 165lbs.

How the car is driven:
Her drive to work is about 2 miles each way and she rarely drives further or warms up the car. We live at the top of a hill which she goes down, coasts in EV mode about a mile on a flat stretch, then up the hill to work. Probably the roughest life style for any vehicle We live 90 mins away from the closest Toyota dealership, so regular maintenance wasn't happening until I started doing oil changes about a year ago. She went very, very far stretches without oil changes (1yr+).

Long story:
Id noticed it sounded rough, but she insisted it was normal over the last month and I'd been pushing to install an oil pan heater but hadn't gotten her go-ahead yet. A few days ago she got a low oil pressure light on the way in, but was 90% of the way there. She consulted me, and I told her to check the oil on her way in, but she did not. On her return trip home near sunset (sharp temp drops), she called me, and I told her to startup and listen to it then shut it off. She did and it sounded rough. I advised her to bring it home, coast/EV as much as possible, and check the oil when she got home as I suspected it was just cold oil.

Next day we actually checked it and found the creamy oil symptom. I drove her in to work in my GX470. Since then, I got a compression tester and coolant exhaust tester, but the days are short and weather is cold. I tried to run the compression tester, but with the No1 and No2 (Fuse 1 and Fuse 7 on the pass side fuse box) pulled it wont start or talk to my Tech Stream laptop for the engine ECM. Putting them back in, but with all the plug removed, I can talk to tech stream/ECU I think...but when I try to put the car ON the engine immediately cranks. What's bizzare is that it seems to run with all the plugs pulled. I have no idea how that is working, but it will "run". I hope someone can explain that.

What I need:
-How can I disable the fuel pump and do a compression test? There are like 7 or 8 fuses labeled "EFI" and clearly some too important to pull and run TIS.
-How can I put this thing into Diagnostics mode without actually cranking the engine immediately?
-Why is one cylinder blackened on the inside if this is in fact a head gasket failure?
-If it is a head gasket failure, does anyone have the procedure on how to replace it? I know an engine swap is better and of equal cost in a shop...but I can fix the head gasket in my garage for $200-300. I cannot swap an engine, so it would be almost 10x as much cost for me personally.

Bonus: If we end up replacing this thing, which she loves, we're looking at good snow vehicles rather than a new prius w/AWD (too little clearance - we got 2 feet of snow in 36hrs recently). Any opinions on the Lexus UX 250h or similar? I think she tends towards light and nimble vehicles, and AWD and some clearance would be nice. Anything that has that, and that could plug in, run EV mode for 2 miles up some serious hills at up to 30mph would be awesome. Teslas aren't really an option here because they weren't designed with snow in mind. I think she needs a GX460

Again, thanks for reading

 

We met in Virginia, in the Hampton Roads area a few years ago. Back then, when she'd just gotten the vehicle, she was commuting quite a bit more frequently and longer distance. Typical city life. Since then with the cold and short commute, it's not the best vehicle now but why fix what aint broke, or wasn't broken. She fills up 4 times a year, at $18 a fill up, and it works out very inexpensively with insurance and local tax code.

No recorded oil burn up before I started. But I changed the oil twice, about ever 9 months with name brand, high mile, full synthetic 0W-20 Valvoline I think. She doesn't check it ever. IIRC the last time I looked at the oil it was darker than I'd have liked to see, but not terrible, no smell or anything memorable about it. No leaks to speak of.

Coolant I'm not sure, didn't look low and there's a bit at the bottom of the overflow reservoir. Unfortunately it's parked on a sloping driveway so it's not possible to get an accurate read on it. I can put it back together and drive it a bit if it'll help narrow down problems.

Is there a way to finish the compression test with techstream? I have a coolant exhaust gas test kit in hand already.

 

Could be, but the creamy foaming oil and really rough run what kind of kicked his into motion. If I can finish the compression test I could verify the head gasket is intact. Which fuse can I pull to to crank the engine without fuel? The 1st and 7th (EFI No1 and EFI No2) fuses disabled the engine ECM.

 

Just to update - I returned the rented exhaust in the coolant checker and compression checker. Came back put new plugs with a touch of anti-seize and torqued down.

As far as I can tell, the Prius C torque spec for the coil packs is 10ft-lbs without anti-seize and 8lbs with. Prius C torque specs for the spark plugs is 18ft-lbs without anti-seize and 15ft-lbs with.

I drove on back roads and country highways for about 20 min, parked, checked the fluids. Coolant was just below the "LOW" line, oil was still foamy. Went home. Performed an oil change with Valvoline 0W-20 synthetic high mileage, new mobile 1 oil filter, new crush washer. I let the oil drain for a few hours with a space heater pointed at it outside in the sun. Pan was warm to the touch afterwards. Put about 4qts in, tightened everything, and drove the same route and its still a bit foamy, but it could be residual. No low oil pressure lights now. I suspect it was the moisture+oil that overfilled the system and caused the warning lights in the first place.

Wait and see now.

 

Monitoring the oil now to see if it foams up. Didn't get to check yesterday. I assume these are like most other modern vehicles, run the car up to operating temps, then cool for 5 mins and let the oil run back into the pan, then check the oil? It still looks a bit foamy, but I also think there is probably still some residual moisture in there.

Thank you for the manual! I just happened to find the torque specs for the hold down on the coil packs at the same time as the plugs...that and the wrench was near by, closer than the 3/8th ratchet. I just touch w/e I'm working on to the brush handle in the jar of anti-seize in place on the threads. I can't think of anything comparable to small quantity I use. But its very little. I work on the other two vehicles in the OP. Done a lot, CVs, new calipers, pads and rotors and brake lines on the GX. Timing belt for the GX is next up, and then possibly struts on the honda. I'd really like the prius to be the idiot proof one that just works.