Depending on the dfficulty of this event, not using Sniper Shot and just Mordreds Outrage, Dikes defense down and Belebogs attack down could suffice, giving you another option for a ex skill if needed. Summer Brynhildr isn't really tbat good.

Relying on back up in sub slots is likely a bad idea too. The most likely mechanic to kill you is the instant death, if she manages to apply it to you twice in before depleting her rage bar and before your debuff recovery skill CD is finished, it would likey kill your entire main party assuming it hits everyone and has hgh application rate. If your main party dies like that, the sub party wont be any help. That's why it might be a good idea to have Aphrodite in your main. Though this dpends on how difficult it is to push her out of her rage, which I can't see being too hard, raid events are pretty easy.