The Warrior’s Path by Catherine M Wilson

Tamras arrives in Merin’s house to begin her apprenticeship as a warrior, but her small stature causes many, including Tamras herself, to doubt that she will ever become a competent swordswoman. To make matters worse, the Lady Merin assigns her the position of companion, little more than a personal servant, to a woman who came to Merin’s house, seemingly out of nowhere, the previous winter, and this stranger wants nothing to do with Tamras.