Walker raced with the women in the same race as the D Grade men.
"Although the first two days of racing were close, Michaela dominated overall, winning four of five stages," said Hastie.
"Even more impressive was that she finished fifth overall in the combined male-female field.
Walker had a four-second lead over the rest of the women going into the final stage, but dominated the hill climb to reach the line eight minutes ahead.
She and Hastie had spent six weeks training and racing in Taranaki to prepare for the course.
Next on the agenda is the upcoming Manawatu Secondary School Championships, followed by the North Island championships in Cambridge and the nationals in Feilding.