I was grinding for spectral ash and decided to change to another ring I got from the chest (Jaguar’s gaze of creeping death → X’fal’s corroded signet) before summoning Andariel again.
After the usual boss fight went pretty quickly, this happened at the last stage: https://youtu.be/zm-WhMuAwzg?si=EW_848_oDGoE5sx-
She didn’t take any damage whatsoever anymore after about 16% of health remaining.