Bump, I have the exact same problem, she's unbeatable.
Same also occurs in Hall of Echoes, Sassan is unbeatable due to an attack that does >1500 damage over the course of a few seconds.
In the remastered version, it seems that the shield charm you pick up in Aleroth reduces boss damage in the Hall of Echoes. Try and see if it works in Ego Draconis.
