Oh wow, sorry for your loss.

I've had situations where when checking in, my cabin luggage was expanded and was fine, but, it suddenly wasn't when getting on domestic after returning to the States. Hindsight is 20/20, but, as others have suggested, you probably would have been better off removing the purse (or, even throwing away the box, if necessary) and just hung on to it during your flight. Or, exploring your CC's theft protection is also very good advice. I know Amex and probably Visa/MCs offer protection up to $10K for 90 days? I'd just file a claim, and let them deal with it.

Regardless, good luck. This is a tough situation.