Comes with three triple up epic adds. These pose no large threat and can be tanked all at once with your MT. Burn the adds down and move to Sariah.
Sariah goes through four stances: Warrior, Crusader, Brawler, and Desperation.
She will nuke for Divine damage if there is target that is not of the specific archetype for stance she is in. Yes this is a 3 tank fight for the most part. Can be healed through it until you come to the Brawler stance (if you have the gear for it) where there will be a lot more heals needed if a Guardian or Zerker is tanking and not a Brawler during the Brawler stance.
Eventually the right balance of healers should be easily up to the task of healing through this mob with one tank. But as you are learning the encounter and you can spare the DPS. Best to learn the fights mechanics.
During Desperation stance Sariah will memwipe frequently and her dps will increase. During this last phase it comes down to how fast you can burn her dead as you will not be able to put up with it for long.
Good Luck.