My 4 year old SWEARING! help?

my 4 year old daughter comeback from her dads every weekend saying swear words, , i have tried talking to her dad about it but it just does not stop, shes say awful words, racist and she going to kill me and she hates me, i don't know what to do about it, i don't know if its her dad teaching her it or his stepson, has anybody got advise how to help me stop her please