Cattery.
My cat hates the cattery.
We decided to try the bathroom transition route.
We had packers in day 1, and she was fine. She disappeared overnight - and was found wriggled between the packing boxes.
We then emptied our bedroom, and shut her in there with the ensuite. She often gets shut in rooms, and just waits quietly til someone realizes. This time she went absolutely bonkers until I sent the kids to sit up there with her too.
She was her normal protesting self in the car, waited paitently in her carrier while the removal guys unloaded, and was fine as soon as we released her. But the packing side wasn't great.
The cattery we use is runs all next to get other. A row of garden sheds at the back, with a shelf to sleep on, food, water and a litter tray, a window, and a catflap. In winter they shut the shed door and have a heater. Then they have a similar sized patch at the front (with solid, clear, panels between the neighbors) for a bit more space. As much as anything, I trust the owner. Been using her since around 2000, and never had a cat come back with fleas etc.
I'd go look at a local cattery (or 2 if you've got them nearby) and see.
From what you've said, you stand a chance of her hiding and not being able to find her. You also risk her bolting out if your friends door if they aren't very careful.