Slipstream is a frontal beam spell you can dodge by strafing left or right or as others have said running through her you just have to be watching and move early in the cast. Garuda can be main or off tanked with Ilvl 55 armor and hq lvl 48/49 jewelry as long as the healers are decent. One other thing about Garuda she will cast a spell on the #2 target on her hate list if it's a healer or dps and they are far away from her she will leave the mt and run toward them so the off tank needs to try to stay 2nd on hate to keep it from happening.