My advice would be just to go with the flow. How long have you been going out? The closer you get to each other the more open you will be. ENFPs tend to be understanding individuals anyway, so don't be afraid to just talk about everything to her. I'm an introvert but even I believe good relationships are based on talking and trust. This is particularly necessary if you are feeling down, because if you don't talk to your girlfriend about it she'll jump to the conclusion that the problem must be something to do with her.
I'll third the suggestion that she might even become more introverted herself. Introverted as in a bit calmer and more pensive, although I highly recommend you open up more. As couples grow closer the differences in their personalities even out, so don't worry too much. Plus, she's with you so she obviously likes you as you are!
EDIT: Sorry if this seems a bit late...I missed a whole page of the thread out.