Two places to really fight her. One is against the huge mushroom in the middle of the zone or other is against the lower waterfall in the river against under the side of the bank closer to the mushroom. Treah has a knockup and an AOE root so plan your pull place accordingly.
Main thing here is the adds are heroic but hit very hard and very fast. Have a summoner pull the mob using their scout pet which dies fast and wont put any ae dots on the mobs like a mage pet can. That forces Treah back towards the raid across the bridge that goes over the river. Once they reach the bridge a enchanter will ae mez the heroic adds in the encounter. Important to note is to have the tank or dirge if you got one in the MT fire a arrow to break the mez off Treah if it hits her also send in the shaman pet. This wakes up Treah preventing the lessened duration of mez from the epic mob which will in turn wake up all the adds as well if the mez runs its course on Treah. Have the MT rescue her and run her to the spot the MT group is gonna be setup at.
Now she will drop buffs has a ae arcane based that will root people in place that is uncurable but you have a few seconds after it runs its course before she recasts it. Also another arcane ae not sure on the name of it that does moderate damage nothing earth shattering at all. She will also strip buffs but easy to maintain debuffs on her while the dps is on add duty to keep the MT alive until the whole raid force is together. One at a time break those adds with preferrably 2 enchanters up there keeping the rest of them locked down with single mezzes. Make sure no one does damage to them to just ensure no adds are accidently broken early. Prolly can take a few on at a time it does happen if a mez does get broken or resisted and it is not to bad but depending on how healers are split between the MT and ST to many on the ST might overwhelm the healers.
Once adds are down and you are not rooted go to the spot Treah is at. If in the river make sure you all get down there and up underneath the ledge and stay there without going into the actual water. She can knock you up out of it and root you on the opposite side where Wuoshi will path by. So if that happens as he wanders by the raid will wipe from this. Very important if fighting her down there to watch where everyone is at. Other then that just nice steady dps on her. Your main tank will tend to lose aggro on her when she drops all her debuffs. So make sure you are snapping that aggro back and reapplying debuffs as quickly as possible.