She's just a narcissist. Narcissists love their children only as an extension of themselves, so Lawrence gets all the love because he makes her feel good about herself, having inherited her looks and being a son of the Emperor and generally being authoritative. When the meek Artezia gets in her way, Miraila hates the idea of this less beautiful and subservient extension of herself who doesn't make her look good going against her. But when Artezia doesn't go against Miraila and makes big moves like getting closer to the powerful Grand Duke, Miraila feels good about that and will express love for Artezia.