@CivilSky Now this is just a theory I have but hear me out.
It's heavily implied in earlier chapters that elise and melida were switched at birth in order to bring shame to the main house and honor to the sub house that the maid othello serves. It's a fairly reasonable explanation (given that both of their birthdays are the same day) as to how the sub house obtained a paladin level child while the main house was left with what can only be described as someone more befitting to live in the sub house.
It's entirely possible that the head maid is not only aware of such a switch, but given her age might have been part of it from the get go. She likely believes that with Elise being a paladin that the sub house will be elevated to the position of main house because melida is no true heir to the main houses legacy.
Again that is just my theory of what has happened behind the scenes and only time will tell if i am right or if melida's mom really did have an affair (something i doubt cause elise and melida look fucking related so they likely have the same family blood running through their veins).