I'm 99% sure it is
NOT Philippa Eilhart. We know this because in The Witcher 2, she has dark brown hair. She was also described as having dark hair in the novels. The game developers have done a great job keeping the history and characters in perspective. Probably as good as you're gonna get in a game/novel series. I initially thought it might be Ciri because the game takes place 10 years after the novels, but then dismissed that when I researched King Foltest's Royal Council.
The woman is Keira Metz. Here is a copy of the transcript in the beginning scene in Chapter 3 where Triss is talking to a mysterious blonde sorceress:
Triss: And not just him. They're all eating out of my hand. I regret that Foltest is away at the summit, but I trust you'll tend to the kings' council.
The key word in the transcript is king's council. You're only going to be at the kings council meetings if you're an adviser to the king. And coincidentally, there is a blonde sorceress on King Foltest's Royal Counsil by the name of Keira Metz. Keira Metz has ties to Geralt, Ciri, and Triss from the novels. She was there at the coup on Thanedd Island.
King Foltest's Royal Council:
The king's Royal Council includes the sorceresses Triss Merigold and Keira Metz, as well as Fercart of Cidaris, Willemer the Priest, Bronibor and Hereward of Ellander. Foltest and Demavend of Aedirn joined forces to fight Nilfgaard, but the emperor Emhyr var Emreis was also prepared to fight and met their challenges blow for blow.
Keira Metz' profile states:
Keira Metz is a petite, blonde sorceress from Carreras, who likes to wear an ankh pendant. She is an advisor to King Foltest of Temeria, along with Triss Merigold and Fercart. She is of a very fiery nature and quite fearless. She makes aphrodisiacs and is considered to be a nymphomaniac, at least by Sabrina Glevissig.
During the coup on Thanedd Island, she was literally hurled out of a window by Artaud Terranova, landing on Geralt who was passing below looking for Ciri. Later, Keira became one of the youngest members of the newly formed Lodge of Sorceresses.
I laughed when I saw nymphomaniac. Especially when Geralt sleeps with almost every chick in the game, lol.
King Foltest's Royal Council:
Triss Merigold - It's obviously not Triss
Keira Metz - Blonde Sorceress and Advisor to King Foltest
Fercart of Cidaris - Dead
Willemer the Priest - Male
Bronibor - Male
Hereward of Ellander - Male
By the possibility of elimination, the only logical conclusion is that the mysterious blonde woman in the mirror is Keira Metz. It's elementary! Stupid quote from Raymond Maarloeve.
eace: