In the wiki it says that you can use mirror stance to learn Dragon's Breath, Lunge, Double Attack and Driving Thrust. I have Mirror Stance, but when am I supposed to use it?
Fight her at the winter city quest climax. After the fight with Alissa you'll have to go up to the second floor and then proceed. Select the option to fight Kas. And learn unbreakable and focus on survivability. She does a lot of damage. I've never gotten dragon's breath, but I did get lunge and double attack. I think driving thrust appears as a tome at several points so missing that isn't a big deal.
Fight her at the winter city quest climax. After the fight with Alissa you'll have to go up to the second floor and then proceed. Select the option to fight Kas. And learn unbreakable and focus on survivability. She does a lot of damage. I've never gotten dragon's breath, but I did get lunge and double attack. I think driving thrust appears as a tome at several points so missing that isn't a big deal.
All of Kassyra's powers save Driving Thrust are at levels higher (10 for Dragon's Breath and 8 for the rest) than the current cap so learning the powers is practically useless: you can't use them. One expects that an aspect of raising the level cap will be making them learnable elsewhere as not doing this means that people could miss content simply because they cleared Kassyra instead of waiting for a year for new content to arrive. That would feel awful.