I'm using the mod that lets you have all the strongholds. My PC just got through the challenge and now has the druid one... first time you rest in the grove some Spirit thingy comes to you and says you have to kill a troll shamaness named Nilthiri. Ok, find the troll and whack the crap out of her, technically she's not dead though because she still has a red target ring but the spirit comes and says you killed it, blah blah blah. My problem is that no matter what I do I really can't kill the dang thing so I basically had the group just leave when she got knocked to the ground. Problem is that now every time I enter the grove the witch is waiting for me. How do you perma kill it?

You can only permanently kill trolls with fire or acid. When she's on the floor, get someone to fire the appropriate specialist arrows at her or cast melf's or flame arrow on her. However, I would have thought that you would know this if youve made your way through the grove as you must have met some trolls already...

If you didn't know, then thats the answer :) If not, then maybe its a bug to do with a mod...

Cloudkill, death cloud and other acid spells also work wonders against these creatures. Several weapons like flail of ages or blackblood, or the axes with elemental damage are also usefull, leaving your precious arrows in the quiver.

Must be a bug then because I did use the Melf's as well as shooting her with fire and acid arrows. Oh well, guess I'll just have to keep knocking her down when I go back then. Not a big deal really, it's not like she's a challenge.

Could try hitting her with a Death Spell - knocks over most trolls, even if you usually have to finish the job again with fire or acid. But it usually registers them as having died as a result, despite them not *technically* being dead.