Phase 1:

The Lady doesn’t need a tank in this phase, so use the tanks for the adds.

People will get mind controlled like on the Kel'Thuzad fight. CC the mind controlled.
Phase one ends when her mana shield goes down, they key is to properly split dps between the adds and boss.

Ideally one set of adds goes down just as the next one appears.

Empowered Adherents and Deformed Fanatics are a kill priority.

Skeletal Adherents can only be taken down by physical DPS.

Skeletal Fanatics can only be taken down by magical DPS.

The Fanatic Cleave is very dangerous to melee when you got 2 fanatics close to eachother.
The Adherent spell cast should be interrupted

It is best to have physical DPS on Adherents and Macial on Fanatics.

Phase 2:

She can be tanked.

Adherents and Fanatics will stop spawn.

Players will be chased around by Vengeful Spirits. If caught the player and everyone close to him will take serious aoe damage.

Interrupt the Frostbolt cast.

10 minutes till enrage.