Niiya's coach, Masato Yokota, has been publishing her training over on Japan Running News. All three blogs cover her training in roughly the 100 days leading up to the 2020 Houston Half Marathon:

October: https://japanrunningnews.blogspot.com/2020/04/t-minus-about-hundred-days-to-national.html

November: https://japanrunningnews.blogspot.com/2020/04/t-minus-about-100-days-to-national.html

December/January: https://japanrunningnews.blogspot.com/2020/04/t-minus-about-100-days-to-national_6.html