@Arcane Or maybe, and please hear me out, it's none of that and Ayuko is thinking that she wasn't a good mother to her daughter - meaning being neglecting towards her upbringing due to being a single mom - and Asuka is infatuated with her mother due to seeing her mother less but carrying her father's affection towards Ayuko with her (like a twisted from of meme) which then results in the current dilemma of Ayuko.
Or it really is none of that and the author is simply trying to explore the themes of Mother/daughter incest and present it in an interesting manner.
I'm quoting Bakuman here: "If a Manga is interesting it will be popular/successful." - Which basically sums up what some of those authors are thinking, it is all about the entertainment of the readers and less the political/social/normative implications associated with these themes. I mean if I remember correctly none of Asuka's friends think any ill of her feelings towards her kin, right?
So let's say this story exists as a what if which is then presented towards us the readers and we are the ones who have to get invested (positive or negative) in it which will make it either popular or a success...my only questions is: Why are we talking about this Manga as if it depicted real people? Seperate the story from reality and enjoy entertainment in any way you want, that is what we ought to do and your analyses of the MC's is very interesting though deeply flawed due to the lack of Ayuko's interest towards her daughter's advances around the middle of the story - especially after Asuka confesses. Still very insightful.