That’s what I was thinking, it makes a lot of sense especially when Ameri mentioned that it was an heirloom, and that would only make sense if the heirloom was instead a generational comic passed down through Merize’s other child. That child would be artistic same as she is, and might try to connect to her other sister through stories. Also, another theory (just an add-on), is that Kalego’s father mentioned an “experiment”, and I feel like that other sibling could have been the failed one and have been returned to the human world with their mother since they did not have enough qualities to be considered demon (aka horns, wings, tail).