Well Daisy telling no is not about pure mindset, but the fact that mc is her nephew in the first place. It's more about incest dilemma, rather than her being not interested in sex. If it was any other guy she would jump his bone right there in the first bath scene. Also it's a game mechanic with affection points and slow progression. Same with other characters like even Mae that is hitting on him hard, and who had already multiple sex intercourse with mc in the past. But she still refused him, even tho it made no sense.
Btw she is portraied as being the same age as mc, but she is nowhere near loli type character. I know the initial idea was for mc to be shota protag, but milda just can't do it i guess. Same with bestiality, we have some teases like cows milking, their pussy pics for no reason, affection points and Adeera's horse dildo, but no real bestiality. So in the end mc is 18 y.o., even if it's bullshit.