The above girl showed the inner part of her lower lip.
It seems that people say "she curled up her lip".
However, the dictionary say
curl one's lip: phrase of lip
raise a corner of one's upper lip to show contempt; sneer.
So, I think "curl up one's lip" should be like the below picture.
How to express "to show the inner part of one's lower lip" to show disapproval as the girl shown in the first picture?