Why did my friend say I dont understand what's going on with black cruelity because I'm white. Don't you think that's harsh?

I saw videos about people destroying property and black people's lives. WTF is wrong with people?!
See that's why we need to speak out about this! Black lives matter! My black friend (half black and half white) said I'm not understanding this whole thing and people are treating black people like they're nothing. She yelled, "There was a black girl that got killed in her home and she did NOTHING! POLICE OFFICERS KILLED HER! What's does that's have to do with potesting? You don't get it at all! You're not black so of course you don't understand. You're not seeing the real thing!"
She yelled at me. I'm on her said. Why do people think I don't understand? I just wanna help.