Legalities...
"White people should be killed", is a matter of opinion.
I've never seen a statute, that outlaws an opinion.
Now, if she had said, "you should go kill whitey"... she might be guilty of inciting murder.
Had she said, "I'm gonna kill yo' white @ss".'... yeah, that's an actionable threat, and can be charged as such.
Sorry gnome, "White people should be killed." is not an opinion, it's STUPID.
I don't know who this girl was or if she knew or was related to Michael Brown, it may have been an emotional outburst which happen when teens are killed by police gang members terrorists... People say things they don't understand the scope of under circumstances such as this.
Even IF Brown had a weapon, which he didn't, you have to admit that the forensic details (number and placement of the shots) are pretty difficult to justify for an unarmed suspect.
Police have to protect themselves, that doesn't mean shooting someone who has their arms up at distance or continued fire when no weapon is drawn and the suspect is 'charging' or putting more than one round in the suspects head. That was also STUPID. Brown's crime was STUPID, but there was nothing that would indicate that he was armed.
We still hold citizens who 'have authority over other citizens' and an arsenal of non lethal and lethal weapons to A HIGHER STANDARD than 18 year old cigar thieves, and we should. We pay them lots of money.