No offense, but it's pretty clear you didn't read the whole article:
Katie’s sister, Stephanie, is convinced the film writer, F. X. Toole, now deceased, based the film on Katie. Too many similarities, she says.
We don't have enough evidence presented here to say whether her accusation is right or wrong, but we certainly don't have any evidence here that Toole couldn't have taken the story. Note that Katie's injuries occurred in 1996, and Rope Burns was published in '01.
Also, it should be noted that unless we're sure the original story had the euthanasia in it, it can hardly be said to be Toole's fault, and the euthanasia is not propaganda if he heard about Katie and wrote it during her depressed phase. Further investigation is warranted.