How did the bog child die?

When the bog child is pulled from her ancient grave, a noose is discovered around her neck. This would appear to suggest that she was hanged. However, the matter is further complicated by the fact that the bog child—or Mel, as Fergus the archaeologist calls her—appears also to have been stabbed in the back.
In his dreams, Fergus pieces together the incidents that may have led up to Mel's death. It's apparent from measuring the corpse that Mel was a dwarf, and Fergus imagines that this may have had something to do with her death. He dreams that Mel was killed by her tribe because, as a dwarf, she was perceived as unnatural: a freak of nature. Apparently, this was at Mel's own request, as she wanted to be spared the potentially long and painful death of being hanged.