The Jackal himself!
I noticed that too, thought it might have been in reference to some criticism he reportedly received for seeking vengeance rather than the truth. I agree that sentence looks weird, however are there better explanations than Maresca forging it when it's damned likely to come back to her if he is? Unless she's vacationing in Tibet, she might just be paying attention to the case, being with the appeal winding down and all. If he actually did that without her permission, that seems a lot of downside for a fairly minor upside, considering John Kercher has already written four things publicly about the case and he could probably solicit one from him.
Perhaps I misunderstood what you meant, were you suggesting she approved him writing something in her name? Thus she wouldn't protest, but it was him actually writing it? I could see that possibility, but would it matter that much? I've a suspicion that might have happened with Guede's letter, but unless they expose it themselves, how could anyone prove it? What would it really mean even if they had done this? It's an appeal to emotion and attempt to rehabilitate in the minds of potential jurors the DNA 'evidence' and suggest the other 'evidence' is just as damning. It's for an Italian audience, so she might well just sign off on an outline and let him write it in Italian.
It's rather cleverly written in my opinion, I found myself kind of liking who wrote it from an entirely objective position, meaning I bet it is relatively effective with a neutral audience. Let us hope it is not widely distributed, what paper did this appear in, or will it be read in court?