I'm not sure it is strictly true to say she was "allowed" into her room, then behind crimes scene tape, to retrieve her computer. She, apparently, just decided to go get it and no one stopped her. That might simply be a result of the chaos of the day, and the inexperience of Napoleoni who was in charge of her first investigation with the Kercher murder.
The cops simply blew it, and Filomena risked it... but turned herself in.... and had no consequence other than the outrage of the cops!
I believe it was in Dempsey's book that the most full account of this little episode resides. But the compromising of the crime scene was not only this - through no fault of anyone's really, the postal police gave both Amanda and Filomena the run of the place (with the obvious exception of Meredith room which was still, then, behind the locked door.) Even semi-pro-guilt author John Follain said that Filomena was allowed to "rummage" thought her room, whatever that means.
But incredibly, after taking her own computer, from behind police tape, Filomena takes it with her (accompanied by her lawyer) to the Questura; where in my way of thinking the cops must have had apoplexy. If nothing else, this proves there was nothing "secure" about preserving this scene.
Fast forward a bit.... given that Massei's sole basis of conviction in 2009 is on the basis of nuances of forensic found outside the murder room it is simply stunning that the compromised crime scene did not rule out anything outside of the murder room.
The most obvious piece of "compromising" was the claim that after Battistelli and the other postal police saw a dead body in Meredith's room, under a blanket, is the claim that they did not immediately go into to check - I mean, was Meredith injured and unconscious? Did one of them track in DNA from the door-around, where two groups of people had just tried to break the thing down, one unsuccessfully?
Tragically and horribly, Meredith was not unconcious and injured ony... it was far worse. But the point is, from the door way how would you know? But that "scene" was not something a respectable court would have allowed to decide this case at all. Filomena's laptop is only one of many of the issues.