Didn't the company give it to Pippa so Kate could get around the no freebie rule? Kate wore it once photographed shopping (to make sure it was seen and the company got kudos?) and never again.
This is exactly it. Media often tries to link Kate to Diana and often with utter bs stories. Like the sapphire & diamond cluster earrings, on the dm they wrote today or yesterday how Kate's pair is from Diana's collection, though it isn't, as an idiot (or at least someone who has no eye for jewellery) can clearly see that Kate's pair does not match any of Diana's.
That baby commemoration necklace was indeed a freebie sent to Pippa, who then gave it to Kate (and we can guess that Kate receives many a freebie this round-about way).
Oh well... Luckily we have eyes and a functioning brain