That's OK I figured it out over lunch!
The hands refer to the protestants and the catholics being friends, which is what Catherine at certain times in her regency was striving for (Edict of Toleration 1563).
I can imagine her wearing this jewel at crisis meetings - it means: I am the mediator, I am the chairperson. Unfortunately because she changed her tack so often, neither side trusted her.
There is probably more symbolism in the jewel. Renaissance items were always packed with references. The idea was that someone would ask about the jewel, and the owner or wearer would be able to hold forth about the complicated allegories etc.!