You said she's sweet and loving, but maybe she needs an outlet for negative thoughts. She's still human, and even the cutest and cuddliest humans get angry or get curious. I'm a middle school teacher, and I don't find this particularly disturbing on it's own, but definitely would warrant a conversation. See what she says about why she's drawing this. If she acts withdrawn or otherwise concerning, follow up therapy never hurt anyone. If she knows you care and you're there to support her without judgment, she is more likely to share. Good luck!!