Honestly, Aries didn't also know about the seal. She simply helped Violet because she owed the princess and she was innocent. But when Violet sent that seal to her, Aries had a hypothesis about how Violet got that important valuable in her possession.
Violet was just a simple princess from a small valley kingdom colonized by the Maganti Empire. Her ambition in life was a fortunate marriage, to have obedient children, and to help those in need with everything she could. To sum up her life, the only reason Violet got to marry the eighth prince was because of her surname.
In other words, there was no way Violet would possess such an important piece all on her own. Someone… who trusted Violet or just wanted to protect her, gave that to her to gain immunity if the guerrillas finally made their move and overthrew the throne. Or, as simple as using it as a valuable piece for leverage.
