@PrincessInk My character Monsieur Beaumont both wins and loses Arcana Battles, but his battle opponent forgets the battle regardless of the outcome. If they win against him, they'll know because they'll have a new 'card tattoo' of his Roman numeral.
And your character's ability sounds fine because of what Twaggy said, but also because the battles can be anything. If the Arcana Battles were only battles of magic, then I might see that as godmodding. But because battles can be as mundane as seeing who can eat the most cotton candy without throwing up (don't do that; it sounds dangerous), then your character's ability to manipulate magic won't necessarily make her more able to win the Arcana Battles compared to others.
