Elethriel's Elemental Bow was introduced in 2008 as part of an update that included many new quests and consequently, many new items as well. Interestingly, in the same update, an item called Yol's Bow was also created, which also appears to be unobtainable.
Both bows, based on how their names are written, suggest that they belong to someone:
-(Elethriel's - Elemental Bow / Yol's - Elemental Bow).
I have no knowledge of any relationship with someone named "Yol."
However, regarding Elethriel, we have two elves with quite similar names:
- Elathriel: An elf of the Kuridai caste in Ab'dendriel.
- Llathriel: An elf of the Cenath caste in Ab'dendriel.
Elves have various distinct castes, each with its own characteristics and customs. Some are fighters, some are magic users, and others are peaceful.
In the case of Elethriel, he's from the Kuridai caste, a warrior elf, related to weapons and physical combat. On the other hand, Lllathriel is from the Cenath caste, a caste with incredible magical powers, probably one of the most powerful elven castes.
Both castes have something in common; they both inhabited valleys and mountains, most likely in the Shattered Isles. In my opinion, I believe that the quest could be related to that island.
But beyond the speculations one may have, it's worth mentioning that elves also have their own language, and the use of certain elven words is often part of their names.
In this case, we have the following three words: ELE-thriel / ELA-thriel / LLA-thriel.
Therefore, we can deduce that this bow would have indeed belonged to an elf, perhaps a relative of the two elves I mentioned.
Lastly, it is necessary to mention that I have no knowledge of whether the mission is related to one of these elves or the Shattered Isles. Instead, these are just speculations.
Regards.