She fought bravely against a brutal aggressor.
When the Romans came to the Iceni Royal household, she was whipped and her daughters were raped. Many of her followers were outraged by their treatment by the Romans.
She stood up against injustice.
The Romans had a treaty to treat the Iceni as allies. But when King Prasutagus died in AD 60 they went back on their word and demanded money and land.
She was a freedom fighter against a greedy invader.
The Romans offered land around their colonies to Roman settlers. There were so many people being given land in East Anglia that the Romans had to extend their territories and that meant taking over the areas given to their allies.
She was brutal, offering her victims no mercy.
When the rebellion, led by Boudica, encountered a town she ordered that it should be razed (flattened). In the three towns destroyed: Colchester, London and St. Albans, over 80,000 inhabitants were killed, often in terrible ways.
Her fight with the Romans was personal.
Boudica lived in peace with the Romans before her husband died. When they came to take her money and then abused her and her family, she incited others to join her rebellion against the Romans.