This is quoted from my showroom thread. I thought it was fairly helpful:
Originally Posted by Malibooya
Glad you want to learn! Here's why your friend crashed, aside from poor reflexes:
The Focus, unlike other economy cars of its day, has independent rear suspension. Most compacts (and even many mid-sizes) of the time used what's called a torsion beam design, which is pretty much what it sounds like. Basically a piece of steel connecting the two back wheels, so whatever one rear wheel does the other does.
Long story short, it usually means crap handling, and a lot of plowing even when lifting off (understeer). The Focus's rear suspension design allows it to give you what's known as "lift-off oversteer," which is another term that means exactly what it sounds like it does. Combine that with the Focus's short wheelbase, and you've got a lively little car even at base model trims (like your SPI).
So what probably happened: your friend was descending the hill, came in hot and lifted off while cornering and felt the rear go light. She panicked and slammed on the brakes, which caused the rear to come around even more. And BAM. There's your crash.
And this is what it led to, in my case. Stay safe out there