Correct me if I am mistaken but since you are trying to price a forex option, wouldn't it be more appropriate to use the Garman and Kohlhagen extended Black-Scholes model since it better copes with the presence of the two interest rates associated with each currency respectively?
"Also, LIBOR rates were considered a useful measure of the risk free rate (the rate taken closest to option expiration) due to its proximity to the overnight indexed swap (OIS) rates. Since 2007 however (and as a result of the financial crisis), the LIBOR-OIS spread has spiked and become unstable . John Hull has a very popular paper on this topic."
John Hull said: "Most derivatives dealers now use interest rates based on overnight indexed swap (OIS) rates rather than LIBOR when valuing collateralized derivatives. For non-collateralized transactions, most dealers continue to use LIBOR rates for valuation."
Most of this information was taken from a thread with the link below:
Risk Free Rate vs LIBOR