In quests like these with different characters (not just Galiene), you either have to give up or win with experience and skill.
Therefore, try both options in turn. But before starting the battle, make a save in case the monster turns out to be evil.
The exact set of advantages depends on the type of opponents, but generally you need:
1. Willpower (80+ %)
2. Speed (10+ %)
3. Arcana (10+ %).
The lowest scale usually adds problems if the monster gains an advantage.
You can improve these parameters with the help of clothing, artifacts, experience, and experience in using artifacts.
Some monsters require you to drink a potion first.
This is described in more detail in the library, not far from Celica’s house.