In section one of The Sweet Hereafter, what thoughts were distracting Dolores that fateful morning?

The Sweet Hereafter is a story which depicts the death of fourteen students caused by a school bus accident. Dolores Driscoll was the driver. In the beginning of the book it was described that Dolores was distracted with the thought of having seen a stray dog in the street. In her effort to avoid it, the bus went ot the other side up unto the icy water.