This is like the easiest gold key I have done... Stand in one spot , everyone standing in healing springs, when she ports to you and drops aoe run to other side and drop more healing springs, all while they are dpsing, rinse and repeat, ultimate heals when needed. Easy win.

Personally I would suggest removing all those numbers floating all over the screen so you can actually see Vila Theran. She gives you ample warning and telegraphs when she's about to do her most powerful group-wide attack. That in turn gives you plenty of time to start building up your Illustrious Healing under the group. If you're a templar ensure you have Purify Light or Channeled Focus or similar active, so if it still looks like a party member is going to fall you can also use Breath of life to keep them standing.

The key, as far as I can tell from experience, is actually watching Vila and being pro-active to her primary attack, and you will have little trouble.