I agree with you totally that it's unlikely that *even* AK and her family were stupid/arrogant enough to override advice from their local lawyer, who demonstrably would know more about Italian law (and, indeed, criminal law in general) than they did. Which, as you say, only leaves the option that the lawyer either advised or acquiesced in the matter of statements, diaries, letters and prison conversations after November 7th.
If the lawyers did indeed think this was a good strategy at the time, I'd definitely question their judgment in this regard. Obviously, as discussed previously, sub-judice rules don't apply to a great extent in Italian law, leading to a whole load of leaking and character analysis. Perhaps they decided on a "fight fire with fire" strategy to try to redress any real or perceived imbalance in the stories being fed to the media. In any event, I think history shows that they were wrong. I don't think that Italian jurisprudence theory differs so much from Anglo-American theory - in other words I think that the generally-accepted principle that accused parties will protect themselves best by remaining silent at least until a trial (and often throughout the trial as well, incidentally), holds true in Italy as it does in the US or UK.
I think that the addition of an American lawyer to AK's team will likely - and correctly - result in a far more controlled use of AK on the stand (whatever some people might think of this new lawyer's credentials in general). However, I think that to an extent it's a case of "shutting the stable door after the horse has bolted" - i.e. the court statements, diaries, letters and prison conversations are already out there, and have already done the damage that could easily have been avoided.
By the way, I'm not making these points as a cheerleader for AK in any way, and nor do they imply that I think she's non-culpable. But my points are made to illustrate that I think her lawyers could and should have protected her better. Whether it would have made any difference to the verdict is both moot and difficult to gauge.