George R R Martin on Elden Ring's lore.
[Warning: The following article contains spoilers for Elden Ring.]
St. Trina is one such figure that is mentioned only in item descriptions, although there are several pieces of equipment that are tied to St. Trina which gives players a more complete picture than some of the game's other mentioned figures. It would be easy to assume that St. Trina is just a background character created by FromSoftware and George R R Martin to help give some extra detail to the already expansive backstory. Details surrounding St. Trina are sparse even in the item descriptions, "St. Trina is an enigmatic figure. Some say she is a comely young girl, others are sure he is a boy" is included in the item description for Elden Ring's Sword of St. Trina.
However, there are some big clues that St. Trina is in fact a character that players can actually find in the course of the game, the Empyrean Elden Ring's toughest bosses Melenia and obtain the Remembrance of the Rot Goddess, which states "Miquella and Malenia are both the children of a single god. As such they are both Empyreans, but suffered afflictions from birth. One was cursed with eternal childhood, and the other harbored rot within."
Elden Ring's St. Trina Is Probably Miquella
A further link between the two can be found when looking at the Fevor's Cookbook item set, according to their description were penned "by a man who was utterly captivated by St. Trina. He continued the search for her in his slumber." These key items are one of many Cookbook sets in Elden Ring, each with its own theme, but 
Fevor's Cookbook [3] is actually dedicated to a single item, Bewitching Branches. These items stand out as having no relation to St. Trina, with the item description instead stating that the item is a "Tree branch blessed with an incantation of unalloyed gold. ... The Empyrean Miquella is loved by many people. Indeed, he has learned very well how to compel such affection."
In regards to the confusion surrounding St. Trina's gender, this could largely be put down to Miquella's appearance, as seen in the opening cinematic being abducted by Mohg. Miquella seems to have a rather feminine appearance, which could easily lead to confusion amongst followers who weren't aware of St. Trina's true identity. Players who find the Golden Order Principia in Elden Ring will also be able to learn the incantation Radagon's Rings of Light, which states "the young Miquella abandoned fundamentalism" which could explain the sudden disappearance referred to in the Sword of St. Trina item description.
This item also marks this moment as "the beginning of unalloyed gold," which could serve to explain why the Unalloyed Gold Needle treats Elden Ring's Scarlot Rot.
Elden Ring Cut Content Points To Miquella Being St. Trina
It is also important to note that, according to metaketaweta on Reddit, cut content has been discovered within the game that explicitly confirms this truth via an unused NPCs dialogue, but given that this has been cut from the game, it's unclear if it remains a canon piece of information, and as such it cannot be considered hard evidence at this time. FromSoftware is known for putting some of these curious character relations into its previous titles, such as the popular all-but-confirmed theory regarding Dark Souls 3's Nameless King being the oft-mentioned Firstborn of Gwyn from Dark Souls, but given FromSoftware's silence on even its older titles, it's unlikely that players will get a definitive answer on this subject unless Elden Ring gets a DLC focused on the mysterious young Empyrean.
Given how big Elden Ring is, and given FromSoftwares history of DLC entries, it seems likely that Elden Ring will receive at least one expansion to its already huge base game which may see players given some more info on some of the more mysterious figures within the lore of the game. However, this is one mystery that FromSoftware may leave untouched, as there are enough clues already in the game for players to make the connection, and any hard confirmation may well spoil the delicate balance the company strives for in allowing its players to formulate their own idea's and theories. That said, there's certainly room to explain more about these characters and still create new lore mysteries for players to uncover about them, and it's always possible that this could be a complete about-face, with St. Trina or Miquella appearing in a possible DLC to disprove the generally accepted theories once and for all. But given the evidence currently in the game, Elden Ring's St. Trina mystery is most likely solved.
Source: metaketaweta/Reddit
