Sounds to me like it's more a matter of FEAR than immaturity. If she wants to go and the opportunity is STILL clearly there, then she should look at this as an opportunity for growth and an indenpendence. If she is a model student, she should take advantage of the opportunity. ENCOURAGE IT! Don't let her see your hesitation.
Maybe there is a little fear on your part, as well. It seems as though you both need to have a chat about each of your fears and how to handle them. What are the positives, what are the negatives? GO WITH WHAT IS CLEARLY an opportunity set in place for her!! Courage is not the absence of fear, but moving forward DESPITE the fear. Fear will keep you from a multitude of things, opportunities, etc in life if you let it. An opportunity for BOTH of you to grow.........individually and in your relationship w/ each other.
You CANNOT protect her from being exposed to all kinds of things, but you CAN prepare her for handling them. THAT is the key!!