After a lonely orphan discovers she belongs to an almost-extinct race that guards the source of all life, she must fight to protect mankind from the only other of her people, her parents killer.

I'm confused on one point: the almost extinct species guards the source of life, and yet the only ones left are killers? How about:

When a lonely orphan discovers she belongs to an almost-extinct race, she must prevent those of her kind who remain from destroying humanity.

Agree with the others. Since these elements have been done before, what sets this apart would come from the details. Next attempt, specify her race, the source, etc. Add the backdrop (where this is, when...)? to help with the mental picture,

There appears to be unrelated facts here.

Lonely orphan. Source of life. Parent?s killer.

There is no mechanism here. Just elements. We also need a goal and some obstacles. We don?t even know how this is going to play out.

A woman is in a fight for her life with a member of her own ancient race who wants to destroy the very thing that allows life to exist.