Playing on PC i can confirm that this missing race NPC will occur if you trigger/start/finish (?) some contract quest from the nearby village Larvik, i had just finished the "Contract: Monster on the High Road/Strange beast" (with the cart in the middle of the road, the cave and nekkers) and the race NPC was then missing (tried to meditate waiting for her to reappear without success), thankfully i was able to get back to a recent save made before triggering those Larvik quests ("Contract: Monster on the high road/Strange beast" + "Contract: Morkvarg/In wolf's clothing") and the race NPC was there, allowing me to race.
Thank to Valhaal for mentioning how to avoid that bug.