Wow Chrissie, you simply look amazing in that avatar pic...so feminine!
I've been on and off NBE for almost a year now and while growth is noticeable I have not lost function. However, as has been stated numerous times, everyone is different so your results may vary.
As for the girlfriend, if you decide to travel down the path of presenting female all the time, you best be sure it's what she wants too. While it's fun for now, the novelty may wear off for her at some point. For me (and plenty others on here) we are or were married with children and "discovered" this much later in life. I think you are very fortunate to be finding out this now rather than when you are middle aged and settling down with life.
With my wife and I we began experimenting with role reversal and toy play early in our marriage; only recently did it lead to wearing feminine items everyday, shaving and more. However, I'm not sure how far she's willing to go at this point...
Welcome to the group, and breast of luck on your journey!