I assume you live in a well and aren't aware of the circumstances surrounding her crime. During a period of civil unrest, she sent one of a series of racist Tweets urging people to set occupied buildings on fire. Rioters attempted to set an occupied building on fire.
We can't be sure that her Tweet, which received over 300k views, was directly responsible for the murder attempt but I'm sure it contributed.
She pled guilty and received a low sentence for the crime, to serve 40% of it. She got off lightly.
I understand that inciting racial hate isn't a worthy crime in your opinion, but the law thankfully disagrees.