On this particular matter (and having just visited the cesspit to see what was written about it there), it seems possible to me that this information may have arrived via either first-hand or second-hand knowledge of Meredith Kercher's grave site. Raper's report states that Arline Kercher is buried alongside Meredith; IMO it's possible (even maybe likely) that either he or someone he knows visited the grave and noticed that Arline was now buried alongside Meredith.
I also don't think that Arline Kercher's death would necessarily have found its way into the British tabloids. Firstly, John Kercher was always the parental figurehead of the two, and (obviously) he was also the conduit into the British tabloid press: once he died, I'd say it was always by definition much less likely that any news about Arline would ever even be known to the British tabloids. And secondly, the main - perhaps the only - reason why John Kercher's death ever got any press traction was due to the combination of a) his friends/contacts within the tabloids and b) the very poor decision of the investigating police to publicly announce that his death may have been the result of foul play.
That aside, I completely agree with Tom in respect of the disgusting (but predictably disgusting) way in which those nutter zealots over there chose to weaponise the reports of Arline's death. Particularly disgusting in my eyes was the claim that "Although Arline didn’t see justice for Meredith’s killers, I’m certain that she, like us, knew exactly who was responsible for Meredith’s murder"
Oh and I don't think it would be remiss also to alude here to the *different* ways in which those pro-guilt nutjobs always chose to categorise, and impute motive to, the marriage breakups and divorces of Meredith's parents and Amanda's parents, respectively.......