Good luck and glad you're writing - also since I just looked this up on a lark http://en.wikipedia.org/wiki/Spandaramet Checked out your Armenian mythology basis and you have some really interesting stuff to draw from there too since the figure represents fertility and wine in addition to the underworld. That's a really wild life-death/birth-death duality.
Don't go straight for the main goal of your villain from the start - give her a means to her end, or a series of tasks she must complete so that she can bring death to the world. The Armenian mythology sounds like one that hasn't been widely used in written fiction or movies, so this could really be something different. Go for it!
Here is a unique way to approach it. Don't think about what the villain WANTS, think about what the character DOESN'T WANT. Same thing? Nope. There are villains who avoid things rather than seek them. Let's look at Snow White for example- why does the queen try to kill her? Because she doesn't want her to be more beautiful than her. Snow White couldn't do anything the villain wanted, and she didn't have anything the villain desired- she was just sort of on the Queen's list of pet peeves. Or how about almost every crime drama where typically the villain doesn't want to go to prison, and that influences all their actions. Or what about a casino owner that doesn't want to be robbed by George Clooney? Sometimes reactionary villains can be just as interesting.
There's actually a noticeable Freudian streak in a lot of old fairytales. So many evil mother/stepmother figures.
Actually it is I who created that article because nobody knows much about Armenian mythology, and since I had lots of books about it, I decided to contribute
Perhaps she is angry that other forces (religion, science, magic, etc.) are making people live longer. If she is like Hades, she would want people to die, and that death is a natural part of the life cycle.
You better know what your villain wants, because that's the very concept of your story! If there was no shark eating people in Jaws, Chief Brody would sit home and do a word find, and there would be no story. The villain's plan IS the story. That, and how the hero or heroes react to this plan. Sauron wants the ring of power. Hobbits take the ring to Mount Doom to destroy it. Without Sauron wanting the ring, there is no story. Hobbits site home eating second breakfast and smoking pipe-weed all day. Not much of a story.