Since everyone seems to have the bases covered pretty well on how she could easily have become legitimately lost, I'll throw out a few points on the conspiracy side of things by combining several of the already-put-forth possibilities.

First off, she died of starvation in only "26 days", but seemingly didn't expend any calories trying to help herself?

Secondly, how do we know it only took 26 days? I mean, is the only "evidence" the date in her journal? Could she not have post dated it?

Thirdly, although I'd never heard of a SPOT device, she had one, but apparently didn't activate it?

And, from Birdwatcher's NY Times link..

Quote
Ms. Largay had adopted the trail name Inchworm, making light of her pace, but that pace had taken her nearly 1,000 miles from Harpers Ferry, W.Va., where she and a friend, Jane Lee, had set off on April 23, 2013. Her husband of 42 years, George Largay, drove ahead and met them in prearranged spots with supplies, and sometimes took them to motels for showers and a night indoors.

On June 30, in New Hampshire, Ms. Lee cut short her hike to tend to a family emergency, but Ms. Largay insisted on continuing.

Later, Ms. Lee would tell an investigator “that Geraldine had a poor sense of direction,” the Warden Service’s investigative report said. “Ms. Lee said that Geraldine had taken a wrong turn on the trail, more than once,” and Ms. Largay “became flustered and combative when she made these kinds of mistakes.”

Ms. Largay, a meticulous planner, was gregarious and made friends easily on the trail. But she feared the dark and being alone, said Ms. Lee, who told park wardens “that George did not know the extent of Geraldine’s inability to deal with the rigors and challenges of the trail.”

But after he reported his wife missing, Mr. Largay told an investigator that “Gerry was probably in over her head.”

Her doctor would tell investigators that once she ran out of the medication she took for anxiety, she could suffer panic attacks.


So we're dealing with an unstable woman on meds that could've run out or been intentionally overdosed on too.