How I retrive a lost password without changing or resetting it
Passwords on iOS are stored in a keychain, like in your MacBook. Here are sevaral possibilies, but honestly, I've never tried any.


Retrieve the keychain from the iPhone backup - when you backing up your iPhone, the keychain is backed up too. This backup is encrypted, so you will need unlock it. Instructions on how to do this can be found elsewhere on the Internet.
Both phones are already jailbroken - the easier way, if you know unix, ssh and command line, but probably this is not your case, and you would void the phone's warranty.


So, it is not an easy task to get access to your girlfriend's Facebook account. ;) /joke/