You haven't really explained this "distance" you spoke of. Are you moving and want to keep correspondences to an email or two a week at best? Do you want to hang out less? Does she want to be friends and you just want to be acquaintances? How close are you now? How often do you spend time with each other? Have you two helped one another, been a part of each others lives and struggles, or just get together casually for a drink, movie, etc? Did something happen recently, once or twice or multiple times that has changed the way you see or feel about her? Are either of you currently going through a difficult time?

I'm not asking because I want all the details. This is to get you thinking. I believe it's important to weigh all of this before you decide how you should proceed.

As I told another member, it is probably better to not disappear. If it is better for her feelings, things such as work, school, life, personal issues can be used as reasons for less interaction. This could take a good long while though. If she has done something, or you feel like you are "moving on" and she doesn't "fit" your plans, maturity, where you're going, then it's probably better for her sake you find a gentle way to tell her.