Ok, here we go.
Melees are practially useless, except for tanking.
Gorenaire's AE is ok; I believe resist gear matters not (correct me if I'm wrong). The biggest part about her AE is it has a slow component.
Levels are what matter.
Have someone kite her around to drain her mana, then she can't cheal. In order to drain her mana, she has to cast on you, so wear your resist gear when kiting. In order for her to cast on you, you have to be within her kiting range. Test it out sometime. Get in range until she starts casting. You know she'll start casting when she stops. When she finishes casting and you get nuked, start running again, but always stay within nuking range. After about 10 or so of her cleric nukes, she'll have none left.
Bring lots of nukers. The more the better. I would say about minimum 3 wizards, 3 druids, though when my guild did her one, we had about 6 wizards and 4-5 druids. Bring a few clerics and backup healers. Enough for one per group.
DO NOT HOLD BACK. Well, hold back some. You don't want to die on your first nuke with 80m.
That's pretty much there is to it.
Also, get someone who has led a Gorenaire raid, or someone well-seasoned in leading raids.
I would say about 3 groups to take her down, with only about 4 melees to have padding for tanking.
Fight on the ice near the border of the ice and desert-grass land.