This include's in-app password authentication alongside unlocking your phone (no more entering your iTunes password!).
I really hope apple figures out a way to solve this problem. I just want to point out that although this sounds sarcastic, there's some real concern here.
I think the solution here is to have a discussion about personal boundaries with your girlfriend.
Buying $80 of apps and songs on a drunken night has never been this easy! :P