As I said above it's just resists, honestly by the time I reach her I usually have most resists at 60+ as good gear start dropping during chapter 8 and it's pretty easy if you upgrade the resist lines. I've facetanked her on most chars, some have enough damage to kill her without her doing much but the ones that were suckier on damage still had no trouble with capped phys. The void knight I was playing earlier had really slow boss killing speed(outdated non optimal weapon and the build is frontloaded with defenses but not much dmg) so it took forever to kill her but with 750hp and 75phys she couldn't one shot me with her blood aoe thing and the rest couldn't actually deal much dmg, so it was just a matter of killing her slowly. I actually got to see all her skills this time and figure out how she works, on most other chars she just died doing only a couple of things inbetween heals.
Respecing for defenses doesn't do that much if you're not like 70% phys resist though, she does have pretty brutal attacks and they're hard to avoid, but as long as you have resist she doesn't hurt much. But a single piece with a T4 phys mod is like 30%, so you only need a couple+a phys resist idol or something and you're good to go. Also having big damage actually makes her easier too, since when she reaches like 66% and 33% she goes and heal, and you can keep attacking her while she's healing so with good damage you just kill her mostly as she's healing, especially if you have 15-18% culling so you skip the last bit after the 2nd heal.