She ordered her brother killed by pouring molten gold on his head. Because he was a dick.
Did she? I remember Drogo just generally being tired of his **** and giving him the crown he "promised" early.
[URL='https://awoiaf.westeros.org/index.php/Viserys_Targaryen']A wiki of ice and fire[/URL] said:Khal Drogo does not let Viserys sit at the high bench but rather tells him to sit with the cripples and boys, and all the Dothraki laugh and mock Viserys. Viserys draws his sword, angering the Dothraki, and threatens Daenerys's unborn child while again insisting that Drogo give him his crown. In response, Drogo has Viserys seized by his bloodriders, melts down his belt of golden medallions, and upends the pot over Viserys's head, fatally but bloodlessly "crowning" him with molten gold.