Imgur comments 2013: http://imgur.com/gallery/bxES7xn
Imgur comments 2015: http://imgur.com/gallery/DcTK8
Stashed in: gifs, G4!, Cosplay!, Anime!, Reaction GIFs!, Best of Imgur
No one on Imgur knows who she is.
She's definitely doing Caramelldansen:
Imgur comments: http://imgur.com/gallery/LDS8Spk
No Imgurian or Redditor knows who she is or what the source of this video is.
Imgur also has these photos on the page but they are not her.
Imgur comments: http://imgur.com/gallery/DcTK8