Just curious were you avoiding her slipstream cast? She stands still while casting and you can run through her to avoid being hit (makes tank healing a TON easier for the healer). Also there is no red mark for this attack so you literally have to watch Garuda to see if she`s casting slipstream. I tanked this as a warrior and didn`t have much issue, we wiped 2x while learning the fight and got it on our third attempt. Also make sure people are spread out far enough from each other and the stone pillars (you don`t want them to take damage) and that you (the tank) use the limit break if needed.

As for my stats I went for a bit more stam then str.