I wanted to start this weekend with a different topic, but a trailer for the new expansion dropped today and u/ElisTheThunderbird suggested making a post analysing who the character in said trailer was.
There are two candidates as far as I'm concerned.
The title "Once Upon a Pyre" and woman's rogue outfit and seemingly villainous attitude suggests Bloody Falka (Falka Krwawa), a quarter-elf Redanian Princess, who started a bloody rebellion that escalated from Redania into the other Northern Realms couple of hunderd years before the events of the books. She was known for her cruelty. She murdered her father, King Vridank and his wife, Cerro along with their childeren. She slept with her commanders, with one of whom she had a child which she tossed Temerian Queen, Riannon (the daughter of Larra Dorren and Ciri's great-great-great-grandmother), who was held captive by Falka's army. Ultimately, united forces of the North supressed the Rebellion, arrested Falka and sentenced her to death at the stake (in other words: a pyre, thats the reason, the title of the trailer points to her). Before her death, she cast a curse that stated that from her blood, the destroyer of worlds, who will avenge her will be born, which was wrongly believed by the people of the North to be tied to the Elder Blood and Ithlinne's prophecy. However as she was Redanian and the woman in the trailer wears a badge with the symbols of the other realms, it's probably not her, which brings us to our second suspect. [Trivia: when Ciri joined the Rats gang (Szczury), she took the name Falka.]
The second candidate is the one that u/ElisTheThunderbird suggested in his DM – Muriel The Beautiful Rogue (Muriel Piękna Łotrzyca), a Temerian countess, mother of the Queen of Cintra, Adalia (the mother of Calanthe and Ciri's great-grandmother). She was the carrier of the inactive Lara's gene, which activated in her daughter (Adalia was believed to be able to destroy bridges by moving her eyebrows). She was known as a beautiful women who seduced a lot of men, which Vissegerd used to spread lies about Calanthe not being the rightful Queen among his fellow Cintrians (to make them stay hostile towards the Nilfgaardian emperor who was believed to be marrying Cirilla soon). The character in the trailer has almost-white hair, just like every other woman in Ciri's lineage, the rogue outfit also fits Muriel as well as Temerian Fleur-de-lis on the badge she's wearing, however the very same badge may also disprove the theory, because it also contains Cintrian lions, and we know that Muriel's daughter became the Queen of Cintra, but it was by marrying the Cintrian King and Muriel herself was Temerian with no apparent previous ties to Cintra. Also, as Muriel's Elder Blood was inactive, she wasn't talented in magic and the expansion is said to be about mages. Anyway, of the two, she is the more likely to be the one.