Something that seems off at first is that Hinoka is old enough to remember her old mother as well as Mikoto’s arrival, but doesn’t remember that she and Corrin are not blood related and finds out about it in the forbidden S support, unlike Ryoma who already knows.
But then thinking about it, and given how the Hoshidans (or at least the Hoshidan royals) put so much value to blood ties that they expect someone who grew up in Nohr to just join them purely because they’re blood related and thus “their true family”, so it makes me think that Hinoka forgot about her true relationship to Corrin as a way to both quell her doubts in the path of life she chose but also to cope with her trauma. And neither Ryoma nor Mikoto were eager to telling her the truth. As far as the people knew, Corrin was 100% an Hoshidan Royal, after all.
But her yelling at Mikoto that she’s not their true mother is something she deeply regrets especially after her death and probably often thinks about in shame, so there was no way she was going to forget that.
