Why don't you two try and file the claim first before sitting here assigning blame this fighting may all be a waste of effort.
No insurance was purchased at addition expense.
AFAIK USPS gives 250 USD worth of insurance with every package, whether you pay extra or not.
it appears the only "free" insurance from the USPS is for Expedited or overnight packages and that is $100 free, it's on the FAQ at USPS