The train driver said he had sounded the horn twice as the engine approached the crossing 5-10 minutes before 4pm and did not see anyone as they passed the bushes and fences close to the line.
They were approaching a bridge at Awatoto when he and his rail operator were advised a member of the public had told police a train may have hit a pedestrian.
They stopped the train and discovered evidence of the impact.
Judge Marshall, determining the driver was not fault, said Ms Boswell, who was 55, was wearing a "hoodie" and a large hooded rain jack, with both hoods over her head.
Police believed it would have limited her peripheral vision and the rainy and windy conditions would have limited her ability to hear the train.
"It seems she was out walking the dog and, due to the weather and what she was wearing, inadvertently walked in(to) the path of the train," Judge Marshall said.