Hmmm....
Words in spanish for car: Automovil, auto, carro.
Nothing comes to mind as slang for genitalia, unless someone was playing a trick on her and told her wrong which is also a very shameful thing to do -- play tricks on people who don't speak the language.
The word "papa' " with an accent tick on the last A is an informal substitute for the formal "padre" - like "dad" for father. You pronounce it pa-PAH. I can't do the accent mark on a computer, so we will rely on a single quote mark.
The word "papa" without the accent mark is as you said, Spanish for potato or pope.
