The Interest Rate Parity Theorem should work because, when one sells a low interest rate
currency to invest in a high interest rate currency and hedges the currency risk: 

The cost of hedging is given by the forward points, which are equal to the interest rate differential between the two currencies 

The high interest rate currency will depreciate 

The profit from the appreciation of the high interest rate currency has been hedged away 

Interest rates are mean reverting, which means the low interest rate will tend to rise and the high interest rate will tend to fall