Disclaimer: I neither own nor claim to own Harry Potter. This is made obvious by the fact that I am writing for no profit. ;)
I seem to have a block on everything else. Thus, this was born.
If the collective mind of the forest could articulate as humans to, she would liken those ten years to torture. To one such as her a decade was nothing, yet those ten had seemed long, endless. If the trees had mouths, they would have screamed in pain as they died. They were unable to stand the very aura of the Thing. It was unnaturally evil. What hope had they against It, natural beings as they were?
It was a disease, flesh-eating, agonizing. It fed on the smaller rodents, consuming their very life-force and leaving their bodies whole – but tainted. Where those remains turned to earth, no living thing would grow.
It came to pass that there was an area that was almost entirely devoid of life, save the Thing and a great snake. The Thing moved and travelled farther and farther out. The blight on the forest grew, and her growth slowed as she suffered and hurt and slowly died.
And then… it left. Taken by a human. It left and it left the great snake behind, but that was no problem. The snake was not evil, merely loyal to It. The forest was relieved as the terrible destruction stopped spreading. Not pleased, for the evil still remained in the earth and in the dead trees, but she was content to merely have the Thing gone.
In the blink of an eye, it seemed to her, It returned. Once again she began the painful process of dying, tree by tree. Its aura smothered her and she tried to twist away; she was suffocating and was immobile, unable to flee. She could only suffer. Suffer, and wait.
When It left again, this time with the great snake, she shuddered and tensed in anticipation of Its return.
It never came back.
She still feels the evil that It left behind. Though it is easier and easier for her to live, to grow with every passing decade, she knows she will never completely recover. It has scarred her for life.