My sister is trying to change the flat on her Cougar but she can not find a key to remove the hub cap. An ideas where that might be stored on her car?

see the manuals

if its there,,it supposed to be with the jack handle,,in the trunk area,,either there or in the glove box,,good luck,,i hope you find it.

try with the tire iron or in the glove box

if it is not with the tire tool in the trunk or in the glove box, check the center console or any other storage place in the car.

Do not think there is a ''key'' for the center cap. Just insert the flat, wedged-shaped end of the tire iron that is stored with the spare tire into the slot b/t the center cap and wheel and pry it off.