I don't really have the rotation down, and I may have also been undergeared (approx/ ilvl 200), but I spent most of that fight spamming the new roll skill Drain. Use shields when necessary. Destroy the gates or mirrors ASAP because they will spawn more and more adds. Kill the adds. Bring your health back up with Drain and pots. When Shatotto's health gets low she will start casting flare with a long cast time. Each hit will take a huge chunk of your HP and debuff you, causing the next one to hit harder. That's when you stop using Drain, pop your shield again, and try to get in as many f4's in as possible.