Man I feel you. I too am dating a party girl right now. She loves to settle down and such but she works hard and definitely likes to play hard.
I'm not quite sure what to say though as it sounds like a situation I'd be asking help on. It sounds like she has reassured you a few times though which is nice. I'd agree with the above poster that going out every once in a while with them would be cool, but who knows, ever night she's not with you is a new experience. If it were me, I'd try to plan a vacation here and there to let her know that you're putting energy into the relationship and expect the same out of her. It's also a good excuse for getting out of the bar scene and into the "world" scene every once in a while
Good luck with whatever happens, girls are tough.
Edit: Btw my party girlfriend recently broke up with me for what it's worth..