Don't know what to do

[Anonymousperson45667]

Hi this is my first time posting anything on here, my partners daughter lives with us full time, as the child's mother wasn't able to look after her properly, just recently her behaviour has started becoming out of control, starting heated arguments with her father, telling her father she wants to stab me. I don't know how to approach all of this or what to do. I've got two other children so this behaviour cannot continue as it disrupts them. Any help and advice appreciated