This. if you fail a parry just hold block and accept that additional damage until you can strike back. Reflecting her lightning attacks helps break her posture and maintain offense. Acid/ decay status helps here too (though I ended up not using any when I actually beat her).
If you're having trouble with perfect parries on some of her weird combos or her charge after the lightning barrage aegis or the perfection grindstone might give you the edge you need.
Yup. I did most of my damage the first time I beat her bouncing lightning bolts back at her. If you can just maintain your health and get your guard damage to replenish during the intervals, you can take her out. Once I figured that out, I stopped worrying about parries unless they were obvious. Just blocked and focused on making sure I hit her at least once at the end of her attacks.
Did the same with the end boss in his second phase.
Ergo-wise, I prioritized Technique, Vitality, Vigor and Capacity, in that order. Then I put the salamander dagger on a Technique-based handle with reach (the one with the broken street sign attached to it), so I could use it like a spear and access fire attacks without an elemental grindstone.
There are two quartz power ups that help with this too: one reduces the amount of damage you take when you don’t perfect guard, and the other allows you to defend red attacks without using perfect guard; you can block them like normal attacks.