Women could not rule the country under Salic law, but she controlled it (the area now in the center of Germany) in the names of her sons. When her husband was still alive, his brother married her sister (both sisters came from what is now Spain, at the time controlled by the Visigoths). The sister Galswintha, however, was not much fun and tried to spoil everybody's fun by throwing out the prostitutes and mistresses. Fredegund, one of the mistresses, managed to get her killed and became the new queen - the beginning of a not-so-beautiful relationship with Brunhilda, who apparently resented the death of her sister. The brothers warred.
After Fredegund had Brunhilda's husband assassinated, Brunhilda managed to snag her Fredegund's stepson instead. The stepson didn't make it. However, Brunhilda managed to rule in the name of her son (by her first husband)until the son turned 13.
After her son died, she ruled again in the names of her grandsons. When the oldest was old enough to rule, she managed to get a lover of hers in high position (by getting somebody else killed), and to get her younger son in conflict with the older. Her younger son probably killed the older, and became the ruler until his death - at which time Brunhilda took over again in the name of her great-grandson - until this youngest king was killed.
Then the army of the Franks and Burgundians joined into one, all shouted together that death would be most fitting for the very wicked Brunhilda. Then King Clotaire ordered that she be lifted on to a camel and led through the entire army. Then she was tied to the feet of wild horses and torn apart limb from limb. Finally she died. Her final grave was the fire. Her bones were burnt.