What method did they ship? Doesn't Fed Ex, UPS, etc. show the weight of the package on the shipping label? If so, the package would be heavier with the wallet so your friend can prove that the box was empty when shipped. Just a thought!
My best friend ordered a bag and wallet from Gucci boutique in LV. The box came - it was empty. What should she do? Gucci is giving her a hard time about it.