Philippa Eilhart is one of the major characters in book series of Witcher, one of the main antagonists of the game Witcher 2: the Assassins of Kings and a villainous supporting character in Witcher 3: The Wild Hunt.
Plot of Witcher 2: the Assassins of Kings
She made a plot against Demavend in order to create an independent country with her puppet ruler, Saskia.
She helped Saskia in rebelion in order to create her independent country. Depending on player's choice she can succeed or not. She puts a curse on her puppet ruler or would be ruler in order to control her and use her power of changing into a dragon.
She's captured by her king Radovid the Stern for conspiracy, treachery and regicide. The king orders to blind her and put her in dungeon. She asks Geralt of Rivia to free her in order to gain her help in curing Saskia from her curse. Depending on player's choice she can be helped or left to rot in her cell.
If she's helped, she escapes.
The Witcher 2: Assassin of Kings
The Witcher 3: Wild Hunt