In the past, Aries approached the forbidden mansion that no one could enter within the palace grounds out of plain curiosity. Her relationship with Abel at that time was still unstable. But from what she knew, or what she was told, it was the crown prince's dwelling.
But now she learned Abel's child, the crown prince was nothing but a part of the history for Abel to take the throne as a bastard child of his bastard tyrant of a father. The father and the child were Abel. Still, she was curious. For some reason, she felt like that place held more value and sentiments aside from the fact it was this nonexistent crown prince's dwelling.
And this assumption simply grew solid when Abel invited her to that place. She couldn't point it out exactly, but that was what she felt. Hence, she agreed.