So you need to bring her HP below 50% (2.25~mil damage) while preferably using RGB as your main damage tool, all the while eating poison orbs, 25k damage, and 100% gravities, before finally killing her off before she murders you?
I am going to guess that the x2.5 damage she gets when below 50% health also affects the Zaerog-summoned 100% gravity which means fuck.
Seems like Awoken Neptune/Ceres/Minerva are going to be good options to deal with her though, since they naturally resist the 25k damage hits, the 100% gravity and neptune even has nigh-immunity to poison, the problem will be bursting her down after you get her below 50% though, since I doubt even 75% damage reduction is going to help much with the 60k damage defour-summon.
Also, kind of bummed that she summons the zombie dragon, defour and zaerog, but not wangren, threedia and beyzul.
Although, come to think of it, if the zaerog-summoned 100% gravity is part of her normal spell rotation, doesn't that mean that, until she's below 50% health, it's counted as light damage? (Which means you need light resist, not dark resist, to survive it.)