Unicorn death

It seemed to be blasphemous for a "mortal to lay hands on a unicorn" , but the blame comes more practically I think in that because she approached and touched it, she distracted it, and that if it hadn't been for her the unicorn might not have been poisoned.

Now that I think about it, it is interesting because nothing like it is ever mentioned in the film. I can't remember if Lilly realized it was shot with a dart, or if she thinks from some bizarre reason her touching it caused it to fall ill and die. It's not like she actually cut of it's alicorn either, but once she overhears Blix and the others reveling in what had happened, she seemed to blame herself as well.

Because she couldn't leave the wild animals who "guard goodness" alone. They were distracted by her presence, which allowed Blix to shoot a poison dart at them via the blow gun.

In the director's cut Lily lures the unicorn to her and tricks it into feeling safe by singing to it. It lets it's guard down and is shot in the process. She wasn't being pure of heart because she wanted to touch it even though Jack told her she should not, therefore it's partially her fault the unicorn was injured/tainted.