Based on the first 4 paragraphs of The Sweet Hereafter, what would you say that Dolores is trying to accomplish?
The first four paragraphs of the novel, narrated by Delores, who had been driving the bus at the time of the accident, are set up as her explanation of what she experienced when the accident occurred. Delores truthfully explains that she is just not certain what it was that she saw: a dog, a deer, just a blowing drift of snow that, in the right light, looked like something she should avoid. Her explanation is not an excuse; she takes full blame for the accident, and she is ready to accept the blame despite trying to explain exactly what happened. She is not trying to escape judgement for the accident, but she wants to make sure that the truth from her perspective is known, instead of being pilloried by the community for some other crime -- such as speeding -- of which she is not guilty.
...there's no point now to lingering over the dog, whether it was a dog or a tiny deer, or even an optical illusion... I saw something I didn't expect out there... the size of a kid in a rust-colored snowsuit, and I did what anyone with half a brain would have done: I tried to avoid hitting it.
(Banks, The Sweet Hereafter, Google Books)
It is this instinct that leads to many road accidents; had Delores had more time to react, she might have judged an animal not worth the lives of herself and the children, and not swerved. However, her instinct led her wrong, no matter what was or was not in the road; although she correctly mentions that most people would swerve, making her action not a unique decision, it doesn't acquit her in any way.