Relevant Talents used:

Mindbender
Desperate Prayer
Twist of Fate (or Divine Insight)
Divine Star

iLvl: 523

When the fight first starts, the boss will be on top of her web and is cannot be attacked from the ground. In order to attack the boss, a Cinderweb Spinner must be killed. This will allow the player use the thread left behind by the Spinner to elevate up to the boss's platform.

Overall objective:
The boss will remain on top of her web until after she has casted 3 Smouldering Devastations, after which she will descend to ground level. The main objective is to kill the boss before this happens, as it is undesirable to solo the boss on ground level (she gains new abilities and there will be a lot of adds to deal with). On the other hand, the boss will automatically descend to ground level when her health reaches 10%, regardless of the number of smouldering devastations that has already been cast. Burning 10% health while on ground level with the sheer number of Spinners adds is close to impossible for a priest, unless VE is available, but I preferred to use VE at other times during the fight and instead DPS the boss down to 11-12% and finish off the rest during her third Smouldering Devastation Cast

Smouldering Devastation:
The boss's energy bar will continuously decrease throughout the fight. Once her energy reaches 0, she will cast Smouldering Devastation (8 second cast) which deals 400k damage. This damage CANNOT be reduced with Dispersion. It is recommended to top up on health and apply PW:S before taking this damage. A defensive CD can be used if necessary (just not Dispersion).

CD usage and healing:
At this stage it is probably best to avoid Flash Heals unless absolutely necessary. My main heals came from PW:S, PoM, Renew, and Divine Star. Mindbender should be used to relieve the healing pressure. Defensive Cooldowns can be used quite liberally in this encounter but not excessively (don't use up all defensive CDs within a time span of 1 minute).