It's a bit early for that, though, if that were her only reason. Her more immediate motivation, I expect, is to be able to give paid speeches and to promote her upcoming book. In other words, to take more financial advantage of her new national prominence than the ethical or practical constraints of doing so while being the sitting governor of Alaska would allow.
But she said during her announcement that, "We're not retreating. We're advancing in another direction."
Referring to herself using the royal "we" does betray presidential aspirations, I think. ("Show us the money, Jerry!")