4 year old talks of suicide

I have a 4 year old student in my class that has been acting out. She climbs on furniture and refuses to get down. She will not follow directions, and instead continues to climb on things or tries to destroy classroom materials. I have to physically hold her to protect her from herself. This last for long periods of time, or until some one else comes to hold her. While I hold her she kicks me and bites me. She refuses to answer any questions or talk what so ever. She is an extremely intelligent child and can be a real joy sometimes, but the minute she you give your attention to another child she lashes out. She has told us that her step dad would beat her, but that he is in jail. We have talked to the mother about all of this. She promises us that it will never happen again or that she is "cured." At school she will tell us that her mom was mad this weekend and she "whooped everybody." I have a feeling that her mother is giving her overly stern punishment. I can tell that she has had some traumatic experiences just by the way she acts in class. Sometimes she shows absolutely no emotion. Her eyes are empty and hardly ever blink. She just runs away and tries to destroy things. Other times she calls everyone stupid idiots, says that she hates everyone and herself. Recently she told me that she was going to kill herself with a knife. We have had to call someone to pick her up 3 times this week because now she is threatening the other students, and they are afraid to be around her. I have talked to her mother multiple times, but it is clear that that punishment she receives at home is the reason she is acting out. If this keeps up she is going to get kicked out of school. What is the best way to help this child? (also we are a non for profit school for low income families, so we do not have a lot of resources, and parents aren't always cooperative.)