WAUKESHA, Wis. (AP) — One of two Wisconsin girls who pleaded guilty to stabbing a classmate 19 times and leaving her for dead to please a fictional horror character called Slender Man is appealing her case.

The Journal Sentinel reports that an attorney for Morgan Geyser recently filed a court brief arguing that Geyser shouldn’t have been prosecuted as an adult because the girl believed Slender Man would kill her family if she didn’t stab her sixth-grade classmate.

Geyser and co-defendant Anissa Weier were committed to mental health institutions for stabbing Payton Leutner at a Waukesha park in 2014. Leutner managed to crawl out of the wooded park and survived. The girls were 12 years old at the time.

Geyser pleaded guilty to attempted first-degree intentional homicide and ordered to spend 40 years in the institution.