Wow. From the story I'm reading it says that line then the particle no then the persons name. So I suppose they are saying the persons hair looks like this mystical creatures'. Very interesting way to describe their appearance. I makes sense as the character is not very nice.
おかっぱ(あたま)【お河童(頭)】 ﾛｰﾏ(okappa(atama))
a ┌pageboy [short bobbed] hairstyle; a short bob.
▲おかっぱにする wear [have] one's hair bobbed; bob one's hair.
▲おかっぱの少女 a girl with ┌bobbed hair [her hair bobbed].
"Tatsu" is a punctual verb, so "tatteiru" expresses the current state that results from prior movements. "Tatteita" is the past form of it, thus it means "stood (at a location)" (more accurately to say, the subject had stood up previously, and the state at that time was "standing").