I remember how ridiculed I was when claiming that the tiara worn by the Countess of Wessex was not the remains of Princess Andrew's tiara
But if Baxter's photo of the necklace is the same as the one Sophie wore is a bit difficult to tell - check out this link - to it seems a bit odd to remove the 'petals' in between the rosettes...
This is design is common (like the fringe tiara design). I once saw a necklace in Bond Streets in London that I thought was the one Sophie wore. I went into the shop to ask - but was told that it was not it...