Well historical a lot of dynastic cultures practiced incest, so its more historical accurate then usual for a fantasy Europe comic.
An earlier chapter stated that Estella mother loved the emperor. The practice of forced marriage is a form of rape, I think it should be obvious if you use a little common sense to see that she mother probably figured if she was going to be forced into a situation it should at least be one of her choosing [pick her pattern, and picking how she ‘reproduces'] She didn’t have a lot of options. This story is really using a lot of clique ,like the mother of the protagonist must die !, but at least their is a plot driven reasoning instead of making her a.)evil b.) died of birth complication.
I wonder if the Elf looking person, is from the same clan. He is blue like the mom....but he also has elf ears.