Aubrey's definitely on it's way up. I'm not sure how high it will rise, but since it's gone from 153 to 44 in the past five years, it's obviously hot right now. It wouldn't surprise me to see it in the top 25 in the future, maybe even the top 15. Whether that's too common or not is up to you, of course.
Between Aubrey and Audrey and their various spellings, there does seem to be more than a few little girls with names that are the same or very similar. Aubrey could easily be confused for Audrey and vice versa.
FWIW, I like Aubrey for a girl, too. It was one of my top names when I was expecting.