She’s also the face of Poot Lovato, a widely shared doctored photo of her that, according to Know Your Meme, originated on Tumblr in 2015.
The TL;DR of the meme is that Poot Lovato was reportedly created to be a twin sister to Demi. It eventually spawned countless memes.
Source: https://www.buzzfeed.com/josephlongo/demi-lovato-poot-reaction