Ok so discord is also full of piss retards. They were all say she sucked ass for PvP, but Lorelei's passive is fucking useful in BO3 whale PvP because ultimates are 100% random.
Her sleep triggers after 4 stacks of Siren Song are applied, and she applies a stack on every basic attack and for special attacks when sleep has been triggered.
Your sleep is guaranteed to trigger and slow them down.
Pic rel is the 3 remaining enemies units asleep.