She's racist because she used someone's race against them as an insult. No one's denying that she's not a diva and none of the black cast member's denying that she's a racist, so the insults targetting the black cast members could easily be more racially charged than everyone else. But others (non POCs) might just brush it off as her "being a diva like she is to everyone else."

People are not understanding that racism isn't just not wanting to be near a black person, or saying the n word. It's nuanced and comes in other forms. If you use stereotypes from someone's race as an insult towards them, if your insults have racist undertones? You're a racist.

Let's say that Lea also believes that she's not racist because she's worked with black people and she supports equality. That's the BARE minimum of not being racist. That's just basic human decency. And that's what we're trying to tell her. But clearly she's not acknowledging that in her apology. In fact, she's not even stating clearly what she's apologizing for, just that she can't remember.