"Urgent accident with straw or montero"

Hello friends
I had a very big problem with a Mitsubishi Pajero or Montero 2001 of Second Generation Motor 2.8 Diesel without turbo. 4m40 description engine, this car is five doors, this weekend that passed my mother led the car and had a very serious accident with it, she was hospitalized and thank God it is already out of danger, I hope that the help they provide me serves many people who can in the future face this type of problem. She tells me what happened like this:
He says he was conducting the vehicle for a slope of not much inclination of about 2 km away. She wore the car at fourth speed and without pressing the accelerator led to 60 km / h. When suddenly I listen to a large noise in the engine I deduce is the increase in the revolutions of the same and the car is accelerated only at an impressive speed to such a degree that the brake was not served from anything. At the end of this street there was a semaphor with many cars. whereby she desidated to climb on a slope before reaching the semaforo and collided with some advertisements. The car stopped by colliding acting its air bags.

I must try to repair the car and I have many doubts.
1. Since this can be repeated. That this problem could be due in the car or what the points to investigate that they could generate this problem would be. assuming that he had been with good maintenance.
2. When giving a problem like this. That the driver can do to stop the car.
3. What type of preventive maintenance can be carried out to avoid this type of problem.

Thank you very much in advance for your support ...
Greetings