Rioting quiets down chatter about health issues and email and Benghazi and whatnot.
A lot of behind the scenes motives here. There is crushing news in the cycle being squeezed out to cover these riots. A bad bloody day for this administration is a good day for Hillary. Her googly eyes, bad temper, lying diatribes, and horrible condition are kept behind the curtain.
1) Riots drive White voters to vote Republican as a law and order measure.
2) Rioting could make African-Americans turn to violence, rather than to electoral politics.
3) Rioting interferes with her own message as it interferes with anti-Hillary messages.
4) Blacks aren't going to support Hillary as unquestioningly as they support Barack Obama. Obama might encourage militants because he has control over the results. Hillary knows they'll be a headache for her so she'd be less inclined to encourage them.
IMHO, she wants to appeal to a lot of the themes of BLM, but fears that she won't be able to control dissident groups if she's elected. But it's hard to say. If she's desperate enough, she just might think rioting will help her.