Forever Fallen

The earth is in ruins, do to a global pandemic that wiped out over three fourths of the entire human population.
The humans that survived the initial illness, became ghosts of themselves, uncontrollable, rabid, their flesh taking on a dark yellow hue.
The best word to describe them would be zombies.
However, instead of mindlessly wandering around moaning about brains, the illness seemed to take on a life of its own.
The humans retained their human intelligence, even after they were infected. It seemed that the illness commandeered it's host, inducing the human to attack another, bite them, and therefore spread the disease.
They didn't bang on doors to break them down, they set up explosives.
When they came to a fence, they didn't bang against it uselessly, they dug under it.
And they were fast, well some of them were. Hopefully you came across the ones that didn't seem to know anything other than walking.
These things are practically unbeatable to anyone who crosses them.
Except for one person. And that's where she comes in.
Her name is Desiree Cerrulia, and she's humanity's last stand.