Can vouch for this as I was in the same run but in a different party, what basically happened was that our DPS going into her final phase was super low, and somehow two of the bird raidwide AoEs managed to go off, nearly wiping the entire raid. A healer LB3 was used, but nearly everyone in our party immediately died again due to a combination of people not avoiding AoEs or too many unavoidable AoEs + poor management of the blood drain tether (I was the highest DPS in the raid you damn Samurai, I'm not gonna forget you hauling ass halfway across the battlefield to pass the tether to me when you could have just gone to the closer off-tanks and I had an unavoidable pink marker AoE on myself and I was already at half HP - and all just so you could save yourself).
During that phase, she just rapid fire spams the same mechanics pattern over and over again, Diabolos in Dun Scaith style, so the fight basically turned into a zombie mass raise alliance having the same two tanks getting constantly rezzed and tank bustered to death, with a DPS getting caught in between from time to time. It just goes Redemption -> line aoe + blood drain tether + purple marker AoEs + floor circle AoEs -> Redemption -> bird markers + purple marker AoEs -> Redemption -> repeat. Or well, some variation of that. Thing is the tank busters come out so frequently in that phase that the tanks straight up run out of mitigation. We probably spent like 2-3 minutes in that phase before we were finally able to kill her, and I'm surprised we didn't wipe with how she was just picking everyone off one by one with the tankbusters.