Just have her keep receipts for the necessities which she purchases. If the bag is located, she can submit those receipts once the bag is returned. If it is not located after 20 days, it is considered lost and she may submit for the fair market value of the bag and its contents. The maximum value covered is approximately EUR 1,100.
Don't waste your time on the phone with IB. Just make sure IB has a solid address and mobile number for your wife.