WAUKESHA COUNTY, Wis. (CBS 58) -- A woman accused of killing the dog of a family she was babysitting for in Sussex, pleaded not guilty by reason of insanity on Wednesday, Feb. 28. 

Court records say on Jan. 26, 18-year-old Kielee Sonnemann stabbed an 8-year-old chihuahua named Batman with a pair of scissors, then wrapped a bag around his head before hiding his body under a pile of stuffed animals and blankets in the room of an 11-year-old girl. 

The incident happened as Sonnemann was babysitting for the family and watching their 4-year-old daughter, according to court documents. 

Earlier this month, Sonnemann appeared in court where she confirmed she was taking medications for a mental illness. 

Sonnemann's next court appearance, a review hearing, is set for May 6.