I take nitro occassionally when there is angina or prior to going to the health center to exercise. Your sister is correct. She should use a nitrate to relieve any pain. Angina (heart related pain) indicates the heart muscle cells are not receiving enough oxygenated blood. To endure the pain without medication can severly damage the heart. The medication dilates the coronary vessels and provides a good supply of blood.
I don't know the shelf life of a nitro patch, but it may no longer be effective, if it has been awhile.