We have surprisingly few sources on Boudicca - essentially, parts of three works by two authors, Tacitus (Annals 14.31-9 and Agricola 16) and Cassius Dio (62.1-12). In the Supplementary Texts volume that goes with the course I teach, all these sources take up less than ten pages. After that, we're in the realms of extrapolation.
Modern accounts tend to be quite credulous and unsophisticated in the way they handle the sources. For a start, they don't pay enough attention to what the sources actually say. For instance, Boudicca's daughters, who, according to Tacitus, were raped by Roman slaves, are often presented as underage. But Tacitus does not say how old the daughters were.
Nor are the contradictions between the sources properly addressed. Tacitus and Dio actually have completely different accounts of the revolt's origins. Tacitus tells the well-known tale of the kingdom of Boudicca's husband Prasutagus being left jointly to his daughters (note, not his wife and daughters, as people often assume) and the emperor Nero, and the Romans moving in, taking the lot, and brutalizing the royal family. (Though it should be noted that Tacitus does not blame the governor Suetonius Paulinus, for this latter incident - he blames centurions and slaves. Suetonius was certainly not actually present when Boudicca was flogged.) Dio's version is all about the recalling of loans, and blames the procurator, Decianus Claudius. The usual approach has been to combine these accounts, while laying the emphasis on Tacitus' version (as Dio's makes for dull history lessons). But to do that without drawing attention to the differences is not a sophisticated approach to ancient sources.
Which leads to the third point that gets overlooked, why the sources say what they say. Almost everything gets taken at face value, except where the Roman sources reflect badly upon Boudicca. So the atrocities that Dio claims Boudicca's army perpetrated in Colchester and London get dismissed as Roman propaganda, but his description of the queen, which is equally part of a presentation of Boudicca as something alien and other to Roman eyes, is accepted without question, because to modern eyes it seems impressive.
The writers' motives get overlooked. Tacitus' history is a construction in which he is critiquing Roman imperialism and presenting it in the worst possible fashion, and in Book 14 he is very concerned with slaves getting above themselves, and killing their masters. So this story suits his purpose. As a result, and given the incident's absence from Dio's account, we don't actually know that the brutalization of the Iceni royal family actually took place at all. Nor can we be sure that Dio's version of the revolt's origins are correct. All we can actually say for certain is that, somehow, the Romans pushed the Iceni and the Trinovantes too far. The revolt certainly took place, and the cities burnt. That's clear in the archaeological record. But the spark may have been what Tacitus describes, it may have been Dio's recalling of loans. It may even be that it's correct to say both factors were at play (which may be what the brief account in Tacitus' Agricola implies), or it may be that neither story has any truth to it.
Accounts need to signal when they are in the world of extrapolation. Connections have been made with the notion of Celtic matrilineality. Now, this isn't a subject I know a great deal about, but it wouldn't surprise me if the evidence was quite thin. For a start, one's on shaky ground if one starts to say "The Celts were ..." This was a very wide cultural grouping, and what Celts in northern Scotland might have done might be very different from the practice of Celts in Asia Minor. There's some evidence, I understand, for matrilineal practices amongst the Picts, but I wouldn't be astonished to find that this had been combined with Roman accounts that the British accepted leaders who were women to produce a blanket assertion that goes beyond the evidence. Matrilineality was very popular amongst certain Victorian antiquarians, and quite a lot of their theories have been shown not to match up with the evidence. Certainly Tacitus does not say that Boudicca's daughters were raped because they carries the royal line, so again we're into extrapolation. It can't be shown that this wasn't why they were raped, but nor can it confidently be asserted that it was.
2) Too nationalistic:
Boudicca is often presented as a 'British' queen, and her revolt is a 'British' revolt (a view the ancient sources encourage). But her revolt actually did not spread far beyond East Anglia - the Roman allies and territories west of Watling Street and south of the Thames were not directly affected. I suspect Boudicca did not think of herself as 'British' - 'Britain' was an invention of the Romans.
In this context, the sack of Verulamium is often underplayed. It shouldn't be. Because whilst Colchester and London were Roman settlements, Verulamium was mostly populated by locals, whom the Romans would have called Britons - yet Boudicca still destroyed it. The only inhabitants of the British Isles she cared about were her own tribe and her allies the Trinovantes.
3) Too narrow a context:
The revolt is only seen in terms of the history of the province of Britannia. But there seems to have been something going generally wrong with provincial administration in the reign of Nero. At the beginning of his reign, there were a number of trials of provincial governors for financial misconduct while in post, charges brought by provincials after the governor's term of office. In every one of these, the governor got off. About AD 60, these trials stopped, and it looks to me as if this is because the provincials just gave up using the legitimate mechanisms of complaint, as they no longer worked. Instead, they sought other avenues for protests, and it is then that we get not just the Boudiccan revolt, but also the great Jewish revolt in AD 66, and the revolt of Julius Vindex in Gaul in AD 68, which, though directed at Nero personally, had definite nationalistic overtones. I'm not suggesting a direct link - but three major revolts in a decade is a bit of a coincidence, and it suggests that there are conditions repeating themselves through the empire.
One day I'll give Boudicca a proper treatment.