How do i tell my grandaugher to stop responding to this woman, this woman gives?

her dirty looks and has called her names, my granddaughter today called her a crackhead, and the woman said i will beat the crap out of you. I have told my granddaughter to ignore her she,s an attention seeker and enjoys it all what do i do to make her listen, she dont do it to me she dont get a response but she will do it to her cos she is younger