Problems with Lilith bossfight

Im having some problems with the fight in t8, i have more than enough damage but her hp keeps jumping back up. She can be almost dead and suddenly at half hp again. And suddenly she takes no damage.

So basicly its a shitfest to see if she manages to oneshot me at random times or not while i try to get the damage inn.

Any tips, tricks, help or insight into this shitfest i would be soso happy!