Potentially a crazy thing to say, but I think that symbolically Rhaegar is like a father to Dany as well as a brother. In the House of the Undying she walks right by the room containing a vision of their real father without comment whereas when she gets to Rhaegar he passes on the Song of Ice and Fire to her as Viserys does to Rhaenyra in HOTD. There’s also something to be said for the fact that Rhaegar’s children are around Dany’s age and are in fact a bit older than she is; it’s a disruption of the typical generational divide between aunt and niece/nephews. These shifting and overlapping familial relations are reminiscent of those produced by the Targaryen tradition of endogamy, as a man married to his sister is thus both father and uncle to his children, but there are other ways in which familial relations overlap and blur in asoiaf as Ned nominally takes on the role of father to his nephew. I know there’s a theory that Rhaegar is in fact Dany’s biological father and I don’t necessarily believe that but I think it reflects the narrative role he plays for her
[Mary’s] transition is more passive in the Eastern Church: it is a Dormition (Koimesis) during which, according to a number of iconographic representations, Mary can be seen changed into a little girl in the arms of her son who henceforth becomes her father; she thus reverses her role as Mother into a Daughter’s role for the greater pleasure of those who enjoy Freud’s “Theme of the Three Caskets.” Indeed, mother of her son and his daughter as well, Mary is also, and besides, his wife: she therefore actualizes the threefold metamorphosis of a woman in the tightest parenthood structure. From 1135 on, transposing the Song of Songs, Bernard of Clairvaux glorifies Mary in her role of beloved and wife. (Julia Kristeva, “Stabat Mater”)
Dany is very Marian to me and she has a similarly triune relationship with Rhaegar in that she named her son(s) after him, would have married him had she been born earlier (according to her brother Viserys, but he was probably right for once), and as I have argued above he seems to take on the role of her father as well
Edited to add: HOTD obviously departs from book canon at various points, but GRRM (rather unsurprisingly tbqh) came up with Aegon the Conqueror’s prophetic dream of the Long Night (source) and also co-wrote the episode in which Viserys I passes it on to Rhaenyra, which is why I mentioned it
