Let me get this straight...this happened once, for the first time, in January, when you started the thread? Now it's happened a second time, four months later? Again just once?

Is it really every time she wears it? It sounded like a new thing in your first post. Has she worn the pendant at other times during the intervening four months and taken it off each time? Because your last post sounds like it was just today.

Eta: and isn't it possible that she starts the day wearing the pendant and then takes it off before you even see it? Unless you are staring at her cleavage, I just can't imagine it has anything to do with you.