That SO didn't work.
I had one of two branches in mind. One is lower, but more parallel to the ground. One is higher, but about a 45 degree angle.
The lower one, while a good 7 feet (?) off the ground, was too low to hang the swing off of an have enough clearance underneath -- I'd have to put the part of the rope with the hook over the branch, if that makes any sense.
The higher one gave me fits in trying to anchor it so that it wouldn't slide. I think if I get rid of the stupid tubes, I can wind it tightly around some smallish projections (like where large branches had been cut off before, leaving a "stump" of about an inch) and that will be enough. It won't last 10 years, but she won't be using it for 10 years. (A year or 2 at most -- we won't be here longer than that.)