Unfortunately I have no idea how to reproduce or even what events triggered it, but on my last playthrough, I headed out from the Seeker encampment and went to save Gareth.
I saved Gareth, went and finished off the Witch, sent pig Feder back to the camp and then headed back to Seeker camp myself. When I returned, the lizard Saada(?) was at the entrance telling me I don't trust Amadia etc...and that I should go talk to Gratiana(sp?).
So I head in, and when I get there, Gratiana is laying on the ground. When I go over, and click on her, she comes up as a corpse. I have no idea how she died, and what events triggered it, but she died somewhere between me leaving the camp, saving Gareth and then coming back. I was level 6, almost level 7. I had source, with two source points filled.
Has anyone else come upon this? It didn't ruin my game, but I couldn't finish her quest.