My SSS-Rank Dragon Bodyguard

All of Valeria calls Princess Evelyn useless: no magic, too frail to walk far. Then her father is taken and her sister's spine is broken. Evelyn lifts one hand. A storm dragon gone for seven years lands and bows, calling her 'My King.' Her own royal sorcerer covets that power. Twenty thousand enemies march. She never casts a single spell.