Princess Adda the White is an daughter of Foltest and his sister.
She died after her birth and was burried but her corpse transformed into man-eating monster called Striga. For years she has been murdering and devouring people. Geralt came to resolve problem with her and lifted the curse from her, making her a mentally unstable teenage girl.
She became sane after years of magical healing. However due to her monster life she remained a carnivorous glutton. She conspired with Salamandra (Witcher) to overthrow her father. When Geralt discovered it she ordered his execution but Triss saved him by teleportation. However she was merely a pawn in Salamandra's game. Roderick de Wett put on the princess the curse again. Player can decide if Geralt lifts the curse again or terminates her.
If Geralt lifted the curse she married king Radovid V the Stern and becames his queen of Redania.