What happened to the empress???

They put her in the back of the cupboard and forgot about her.

the empress only had the authority to meddle with internal affairs in the castle, but the king took away her authority over anything having to do with the princess. So the reason she stopped being relevant is because she doesn’t have enough power and authority to do anything to the princess. Her brother(?) the count is the only one who CAN do anything about her now, which is why he’s relevant now and she isn’t.