2007 Toyota Prius steering problems

This was a first time occurrence for my 2007 prius. I was stopped midway on my mountain, long & steep, dirt driveway trying to park along the rock side. It was too tight to park so decided to continue down to the bottom. I was in reverse and shifted, with my foot on the brake, into drive. The car suddenly bolted forward propelling me through the fence and down a steep embankment to our deck where 12 people were having a dinner meeting. My brakes didn't work, nor did the steering.

Tl* the contact owns a 2007 toyota prius. While driving approximately 45 MPH, the vehicle began abnormally sliding toward the left. The contact attempted to steer the vehicle toward the right but the vehicle would not change direction. The contact then attempted to brake but the vehicle would not stop. The contact was unable to maintain control of the vehicle which resulted in a single vehicle rollover crash. The air bags did not deploy.