I ran this again for the first time in like 2 weeks yesterday and had an absolute awesome JP tank. I knew the fight already since I've cleared it several times already but basically decided to follow his instructions for the fight. Using auto translate, he told us to park our asses in the center of the room and for me to succor/ sacred soil whenever siren decided to do her vanishing act (aka not reappear in center to aoe charm). I just healed us through her charge damage which wasn't much anyway and with Eos out and using fey illumination + rouse + whispering dawn + succor was a complete joke. I've tried dodging her charge attack before the way I would dodge ifrit HM and like someone said, it has such a large radius that it's almost pointless. Just stand in the middle and eat the damage and hope your tanks/ dps are getting to adds fast enough.