Demigods are the weakest form of quasi-deities:
Quasi-deities: A category of weaker divine beings who don't grant spells to mortal clerics, but could advance to lesser deity if they had enough worshipers. This category is divided into three main subcategories:
Titans: The offspring or creations of deities. Titans include the CR23 empyrean, the CR23 kraken, and the CR30 tarrasque.[2]
Demigods: The weakest of quasi-deities, the offspring of a deity and a mortal.
Vestiges: A dead deity who has lost all or nearly all of their worshipers.
Source:
https://dungeonsdragons.fandom.com/wiki/Divine_rankSo if Aylin is a demigod she would be weaker than a Titan and there is nothing to support that her status as an offspring of a deity would make her 100 times more powerful than anything else encountered in the game.
The correct answer to which portal allows you to see Lorroakan is also "The Nightsong is the immortal child of a divine being" further reinforcing that she is a child of Selune.
When Devas die they vanish from the material plane and it takes several years for their soul to return. This is not consistent wih Aylin at all.
Characters like Minthara and Halsin are also not at all consistent with their background in terms of power level either. Minthara is a 250 year old matron of Lolth, and simply a 6th level paladain and Halsin, a 350 year old archdruid who is "one of the greatest healers in Faerûn" is a 7th level druid who can't even cast Greater Restoration.
It's funny because the 5E interpretation of DR says this, but it's seemingly impossible to find any actual named Demigod who is somehow weaker than an Empyrean or a Kraken. On the contrary, most of them have worshipers, the ability to grant spell, personal domains on the planes, and a meandering list of control of aspects of reality itself, like small-time Gods. If you can think of the Demigod whose powers are less grand than that of an Empyrean, let me know.
Now when it comes to Aylin's respawn, I've heard that argument before. There's a pretty major problem with it - Even Divine Avatars themselves, the incarnations of a God on the Prime Material, a world-ending event, require a decent period of time to recuperate their strength before they can manifest again if someone manages to slay them on the Prime. The same holds true for almost any immortal creature we know of, and this is done on purpose to avoid annoying combat encounters on tabletop where you just need to fight all over again for not knowing in advance that a certain creature can "insta-respawn" - This is true of Devils, of Liches, of Master Vampires, of Celestials, and even Gods. They all need some days, hours at minimum to reform.
That leaves us with three options:
A. Dame Aylin for some reason has an infinitely better respawn rate than Divine Avatars themselves or any other being of comparable power in DND.
B. It isn't Dame Aylin's innate creature type which makes her 'insta-respawn', and also prevents her from returning to the Upper Planes upon her demise, it's rather an element of Balthazar's necromantic ritual and Shar's unknown role in her bondage. I don't believe there's evidence of Aylin *instantly* respawning once freed from her ritual circle in the Shadowfell.
C. Once again, likely owing to the necromantic magic at play, Aylin *feels* like she dies and others might think they killed her, but they don't actually kill her. Much like a Troll which gets taken down without finishing it off with fire or acid, she just goes to 0HP with extreme suffering but the ritual props her back up. That's also pretty much the only common type of 'insta-respawn' in DND, the one where you failed to actually kill the creature.
