Could have saved him
By not trying to save him by following him and telling him to stop.
Beware the old guy chewing gum... it's not gum.
yes its too easy to pick a apart. She, for example, could have found a way to detain him at home the night before. But for the movie point of view they had to make it "dramatic".
She could have called the insurance agent and asked him to delay him until she got there.
Obviously she was very confused and not thinking straight.
She knew about the lorry from before so why did she breathe a sigh of relief when the other car missed her husand. Her husband was by a blind crest, motionless in the road, clearly she needs to tell him to get moving. And yet there was a sense of inevitability about her failure to do so.
Like I said, she was confused.
SPOILERS
Not everything in the movie happened exactly the same from one day to the next. It's not like it HAD to be a truck that killed him when the "real" Wednesday came around.
I think another important point is that she probably was convinced, right then, that the premonitions were happening for THAT reason ... to fix her marriage. Notice how happy and relieved she was to be talking to him, telling each other that they love each other and want to make it work. That was her cue that everything was going to be okay. Besides, she had already told him, seconds ago, that she wanted him to turn the car around and get away from there, and he was doing that. She wasn't thinking that the semi would be coming around the corner RIGHT then.
Si no puedo estar contigo, Ya no puedo estar sin ti...share
But had she have delayed him, we wouldn't have had a movie.
In Jurassic Park, the Richard Attenborough character may have turned to a life of philanthropy and not have developed a money spinning theme park full of dinosaurs. But then we'd not have had a movie.