Good question - It must have been a creative decision. The first cross was way too small and the chain too short.

Yes, and it was way more elegant than the other (which was a bit tacky)

I noticed too, and I discovered that Robin Tunney gave her cross from season 1 to a fan. Technically it's supposed to be the same cross all along because it was a gift from Lisbon's mother (who died when she was still young), but I think it's such a sweet gesture from Robin and she must've made that fan so happy :)