Sky News has just carried video of the family (but no capture of Amanda) queuing at check-in at Rome Fiumicino airport. It appears to be confirmed that they are flying to LHR to connect to a flight to Seattle.
The irony of course is that a private jet would have been the quickest and easiest way for Knox and her family to have got back to Seattle. There are no direct flights between any airport in Italy and Seattle, and a private jet could have flown direct from Perugia Sant'Egidio airport to Seattle. A flight plan could almost certainly have been filed late last night, and the flight could have taken off before midnight. Had that happened, Knox and her family would have been in Seattle within around four hours from now. Instead, they had to travel from Perugia to Rome, spend a night in Rome, fly to London, then wait for a connection for a flight to Seattle.
And of course when you add everything up (8 x hotels, 8 x flights to London (almost certainly at full fare), 8 x LHR-SEA flights (almost certainly at full fare)), the added irony is that there would probably not have been a big cost differential between that and chartering a private plane for 8 passengers.