The best way to prove such a thing, unless you have opinion polls that give scientific evidence, is to look at how Boudicca is talked about in the media and how she is portrayed in other popular ways.
One way to see what Boudicca means to modern people is to look at how she is referred to in the modern media. You can find an example of this at this link. You can see that she is portrayed in this link as a
warrior queen, who fought the Romans to defend Britain.
This shows her as a symbol of nationalism.
The media is not the only way in which we can see how Boudicca is perceived by modern people. For example, we can look at this link to a Celtic art studio. Here, she is once again portrayed as a leader of people who had been oppressed. She is said to be
courageous Brythonic warrior queen of the Iceni tribes who united and led her people in a last massive revolt against the Romans who occupied her lands.
We are told of the “terrible insult” against her. We are told that
Boudicca’s name was never forgotten, nor was the pride of her people who resisted the great power of the Roman Empire. The battle was lost, but their spirit could not be broken.
From such things, we can see that Boudicca is such a symbol to many people today. This is not scientific evidence, but it is at least anecdotal proof of how she is seen.