My sister (12) is constantly joking about killing members of our family. Almost everyday when I'm in room with her she says that she’s going to kill me. Yesterday she told me about video on tiktok where girl where getting her head cut off and that she wants to search it up. And today she told our mom that she had dream in which our mom left us so she found and killed her, then she started laughting about it. I'm starting to be really woried . I didn't know where to post this. Please tell me what should I do.

Sorry for any grammar mistakes.