Like Randall Tarly.
And Cersei.
And I guess Olenna Tyrell, who supported her.

No one likely to rebel at this point. Or they weren't. Until she killed everyone in Kings Landing. That makes them more likely to rebel than not. When you kill the armies that stand against you, fine. You can rule through fear by exterminating enemies. When you indiscriminately kill people who are not standing against you, who are not you enemies, you are a threat to the entire realm. That's an instant vote of no confidence.