What should I do about this friend?

So basically, my best friend introduced me to this guy, we started talking, and now were dating. He's german and we were all in a Skype chat and a really sensitive black girl made a messed up joke about hitler and nazis so he said something back. My best friend is Indian and said "you can't be racist to white people" and basically got really pissed at him for no reason. Now this other black girl, finds random guys on kik to talk to and she met one guy and was talking to him for a few days and apparently she loves him. I told her to be careful and my best friend called me a hypocrite and started attacking me for no reason. I honestly don't know what to do. She's acting like a ***** and is talking **** about him even though he's being the bigger person by not saying anything back. She also has this weird ideology that "you can't be racist towards white people" and all white people are racist and it kind of pisses me off. Now mind you, I shut her down but this has happened before and I iced her out for a few days and she apologized. What should I do? I don't want to choose but she is making me and he told me not to risk my friendship with her. I really like him a lot. And also, she bragged about blasting him today and I told her I didn't need drama bc I have exams coming up that I'm already stressed about :/ please help!