I think it's normal - moving to the distant place causes that relationship becomes weaker. The solution is to make conscious effort to maintain it. Both sides should do it, but sometimes one of them doesn't do it (for many reasons). So then, if this relationship is important to you, you have to take action.
I lost lots of friends, because I always expected that they should do the necessary steps to maintain our friendship and I did almost nothing, waiting for they first step.
You should also remember, that everything changes - you have your life and she has her own one.. Maybe your and her paths aren't common anymore?