My friend is dating my brother and she’s mad I don’t care for it.

Soooo opinions ladies.. my best friend is dating my brother. I have a good relationship with my brother so when he pulls fuck shit of course I don’t want to hear her or anyone else talking crap about him. It has made our friendship real rocky and he has always flirted with my friends when they came over to my house. Most don’t entertain it but she decided to start entertaining it. Am I wrong for telling her not to talk to me about anything involving my brother and it’s best she confides in her other friends? I just feel like she chose to make our friendship weird so deal with it? It’s also just super random because before she claimed she was never interested and that he was “ugly” he doesn’t talk to me about their “relationship” thankfully but idk I just feel like she didn’t take a second to think about how this would affect our friendship so like why should I feel bad?