Why not just buy gold bullion and smuggle the wealth out of the country? Charter a private jet, draw up flight plans for a holiday trip to Europe, then load your granny's gold on board, and fly to a reputable financial safe haven such as Switzerland or Gibraltar. You can then place the funds in a diversified investment portfolio, using a few reputable wealth-management firms (plenty of good ones in both countries, or use US firms), and repatriate them to the US at your gran's convenience.
I would recommend not carrying more than 1/4 of the money on any given flight, to protect against an accident, theft, customs seizure etc.
If you are lucky, the dollar will continue to depreciate and the conversion of wealth into appreciating gold will make the whole venture self-financing.
I would not recommend leaving any capital (apart from her home) in a corrupt marxist kleptocracy like South Africa.