You have to remember that in 2007 far fewer people were on Facebook (or myspace), and that it was less common to upload photos in such great volume then as it is today.
And anyhow, regardless of the existence (or otherwise) of photographs of Amanda and Meredith with their arms around each other or whatever, there are verifiable text messages from within 24 hours of Meredith's death. These were friendly messages from Knox asking if Meredith wanted to meet up (sent on Halloween night and the afternoon of the 1st), and friendly replies from Meredith. They certainly don;t suggest that Knox was developing a mounting jealousy or hatred towards Meredith - in fact, quite the reverse.
Knox hating Meredith is necessary for the prosecutions conspiracy theory, but there is simply no evidence of such hatred.
There is a photo showing Knox, Laura and Filomena that has been claimed as proof that Knox must have hated Meredith enough to refused to pose for a photo with her. The problem with that idea is the photo was taken before Meredith moved into the cottage.
As in several other cases of false conviction, the lack of any reasonable motive for Amanda and Raffaele should be a red flag.