While she did strike me as profoundly unhinged (hell, anyone would be after a century in solitary confinement), I'm not convinced this isn't once again Larian being unsure about what is Deva, and what is Aasimar. It doesn't help that celestial and devil genetics aren't exactly completely straightforward in all cases, nor without exceptions. We don't even know if the de facto 100 year prison sentence didn't weaken her considerably. This is the same game where 3 mortals somehow enslave a netherbrain. Additionally, because of gameplay limitations, dozens of characters are "leveled down". Her in game strength cannot be expected to reflect her strength in lore. Larian wrote themselves into a corner here. Make her reasonably strong, and she one turns the boss solo. Can't do that.
https://www.dandwiki.com/wiki/Demigod_(5e_Race)
Strictly speaking, the demigod race would be the best match for a real "daughter of Selune". They also do not age, provided they are supported by their parent. However, they're very clearly described a greatly varied, and aren't even necessarily that OP.
Well, at least in the case of the Chosen, they rely on what would arguably be one of the most powerful magical artifacts in all of existence in the form of the Netherstones and a good helping of Divine favor from their patron deities. However, putting Aylin's mechanical statistics aside, even the fact she could so easily be captured already invalidates her identity, since once again, we're not discussing some minor fluctuation, so even a stronger Aylin wouldn't be enough, since a true daughter of Selune would be like 100 times more powerful than anything encountered in the game.
Keep in mind that the article you linked is a homebrew race, which is noted at the bottom of the page too. It's a non-official fanfic uploaded by a user, there are like 1,000 homebrewed races uploaded on dandwiki. 'Demigod' is absolutely not a 'common' player character race in DND 5E, not even a creature type. There are, however, Demigods in the Forgotten Realms campaigns and lore - all of them are much more akin to minor Gods in terms of both their power and nature, far above anything Aylin exhibits.
https://forgottenrealms.fandom.com/wiki/DemigodThere is likewise a creature type in DND 5E in the Monster Manual describing direct offspring of deities from the Upper Planes who don't quite rise to the ranking of Demigod, which are the Empyreans - CR 23 enormous Titans whose mere presence affects the emotions of everyone standing around them and reality itself. For comparison, an Elder Brain, which the game calls 'one of the cruelest and most powerful creatures in the universe' even without the crown, is only CR 14.
https://forgottenrealms.fandom.com/wiki/EmpyreanMeanwhile Aylin is literally just a deva, as I said before, she doesn't resemble even the weakest conceivable direct offspring of a Greater Deity.
