to the forum, what a sad time you are having, I'm very sorry to read about poor Misty.
I wonder if she could have picked up some poison from a rat or mouse, farm cats can often become victims of pest control.
Cats do pass on with their eyes open, this isn't a symptom of anything specific, the damp paw may have been the bigger cat tasting her if she was already lying on the floor when he entered, it certainly doesn't sound as if she fought with him.
It may be you never uncover the cause of her death, and that won't help you to come to terms with her death, but it does sound as though her passing was peaceful.
Yes, we are all big softies on here, so don't be concerned about wearing your heart on this particular sleeve.