Deadnaming is calling someone by their birthname, rather than what they call themselves now. So essentially Brianna is saying that if called Brianna Wu John Flynt, you are essentially calling her "nigger" or "faggot" or "white cis shitlord"
At least, according to her "logic."
Wonder how her parents feel about that, y'know, the ones that gave her that name and gave her hundreds of thousands of dollars to shit away.
Edit: Just adding an addendum here - I can understand why a person would want to be called by their new name, but I don't agree with how Brianna believes it is such an aberration against a person.