You can use Aqua's heal upgrade to both overheal party members and remove debuffs like the death debuff. I used Yunyun for lightning shield breaks, aqua for healing, overheal, and debuff removable, darkness for tanking and buffs/debuffs and Kazuma mainly just spammed snipe. I also equipped darkness with a mana circlet so she had close to 50 mana and the other one on Kazuma. Also bring healing items and mana potions for you get low and/or when she seals skills. I was level 8 and beat her with just Kazuma left alive when he would have died the next turn and he had like 16 hp.
Another commenter seemed to imply she has a fire weakness in which case bringing the fire damaging items might be worthwhile especially for when skills are sealed if you don't need to use mana or health potions.