My friend is being racially discriminated at work?

what is the burden of proof that is need to prove this, There are many incidents where she has been verbally ulted by two white girls in her office but if she says anything back to them she is the one who is disiplined by the white directors my friend is a manager as is one of the other girls this has been happening for along time no matter what has happened it is always her who is in the wrong in the eyes of the management and is disiplined she has had more disiplinaries then she can count.