I want to buy gift for my sister in a different country

Above is correct.

Apple doesn't permit international money transfers, and gift cards are specific to the country or region of purchase.

Your credit card or financial provider might allow a wire transfer or other form of international money transfer, as suggested above.

Or you might be able to work directly with a friend or relative in the US, and have them purchase the gift on your behalf.

You send her the money for it outside the iTunes Store system.

(199311)

Check the card's documentation or ask your bank what options you have.

(199313)