Took me a few tries. The key thing is that it's a battle of attrition. You've got to wear her down slowly. Move into her damage zone (the darkish aura that surrounds her) give her a few good whacks or drop your DoTs or whatever, then move out and head for a healing memory to restore your health. And pretty much repeat this process. Her health will slowly buy surely go down.
-- If you have to put some distance from her in order to get to a healing memory, chances are she'll do her force overload. Keep out of its AoE range.
-- Sometimes, when there were no healing memories around, running near their spawn points seemed to bring them up for me.
-- If she catches you with her force slam, which does huge damage to you, use your stun-breaking move quickly to get out of it.
-- If your character can off-heal, this can get you out of some tight scrapes...if you've mistimed something and find yourself in a bind.
-- I think if you can manage to time hitting a healing memory while also within Vaylin's damage zone, it will do damage to her. But that can be a tricky thing and sometimes it's better to just get the heal to stay in the fight. Where possible try to kite her to those memories before hitting them.
That's all I can think of. It's just a matter of slowly grinding her health down. Lots of engage and retreat, engage and retreat.
