Y does my b/fs 10 year old little girl hit her head with her fists when she gets really angry at me?

When she gets angry she hits her head and says that she wants me to go jump off a bridge and hopes I die. And she says that she wishes that she could go jump off a bridge and die to it concerns me. She used to head hit head off of the floor etc. What should I do? I've told her dad and he isn't doing anything or thinks it's a big deal. Please help!!!! please send me a response to my yahoo it's tiffanyanderson59@yahoo.com Thanks.