I have all my shammies together and move them as a group when the cloud comes, then chain heal back up. Make sure your camera is looking at them, so you can see exactly when the cloud comes. If someone gets cycloned, dispel it quickly using your pally so that person can get out of any clouds that come up.

In general, don't worry too much about actively tanking; she doesn't do that much damage. The rest of your group is the main priority.