|Before i start, i always give a pro/con review. I'll start with what i liked about something particular, then proceed to give my opinion on how it could be better. I'm better at coming up with stories and fixing other stories than the actual writing aspect of it, so I won't focus so much on the grammar and writing style. I'm more interested in the story, characters and how it flows.
Fantastic start. Very descriptive without getting bogged down in details so much that I wanted to fall asleep. You described your world with just enough to give me a visual, but left enough for imagination. that's great.
As far as the world itself, there is absolutely nothing wrong with the world you've created. It's very classic. Dwarves, Elves, Orcs, magic, a Dark Wizard that was defeated and may yet rise again. It has all the elements of classic fantasy.
And unfortunately, has been done so much, that it also can be lost in the crowd. Why are elves beautiful? Because that's how Tolkien wrote them. Tolkien had such a strong influence on our culture, that many fantasy writers took inspiration from him, instead of creating their own worlds. Now, there are those who have created their own fantasy realms, but not too many.
Remember, there's nothing wrong with having a world where elves are beautiful and live a thousand years, and Orcs that are green and piglike, but why? Why not create your own creatures for this world? And why do they have to look so human? And if you do want elves and orcs and dwarves, why make them like everyone elses? No race is perfectly one thing or another, so why are all elves beautiful and graceful? why aren't there some that are ugly? Or clumsy? and why are all Orcs ugly and evil? Can't there be a noble Orc? Just food for thought.
Then there's your character. I did like the doubts she showed, because they made her seem real. No one is perfect, and when doing something they're not sure of, everyone has doubts, fears, etc. But, she trusts her Mentor. She's obviously strong in magic, being able to take out a troop of Orcs alone.
But why did she kill them? I understand from what you've written that she did it without thinking, but were they a threat? They hadn't done anything to her yet. She even killed the ones that were running away. And her feelings afterward? The elation that she was able to hold another being's life in her hands, and snuff it out? That's the makings of a sociopath. Not that that's a bad thing, all heroes need to be flawed, and it wasn't quite to the point where it turned me off to her, but remember, it's ok to make your hero flawed, it's ok and even encouraged to give them traits that we don't like, it makes them real, but they must always, always be sympathetic. We have to understand what they feel.
Unless, of course, you want to make her a villain. Not the villain, but A villain. Someone the Dark One can get his hooks into. And of course, we all know what can redeem her: Love. Bring someone into her life that draws her back, gives her a conscience, brings her back from the brink. Or just make her a sociopath. You're choice.
All in all, a fantastic beginning. Keep writing, and let me know when you have the next part!!