Can you tell me what level you are and what spell schools you’ve been using? Astraea is supposed to be difficult and is easily the hardest enemy in the game. The other witch isn’t as hard, but she can mitigate attack damage, so you do need to have a solid plan on how to deal damage mostly with auras, or you need to damage output to brute force her. But she’s still a boss I’d recommend tackling around level 6 or higher.
Also, there is an easy mode in the game settings (hotkey H to open the settings) if you aren’t already using it.