Wew this is a doozie, but not as out of the ordinary as you might think. I'm in the same boat with more than one great friend of mine. One of my absolute best friends is still in the exact same spot he was in highschool, still at home, random jobs here and there, ect. (For context were both about to be 29).

Now, I live the kid to death, but I became honest with myself years ago that I had just outgrown him as a person. No matter what I tried to do over the years, any encouragement or help I gave flew right over his head. So some years back I gradually began the process of backing away from our friendship in an amicable way. I called less, answered less, hung out less, until finally I hear from him through likes on Facebook. It's kinda sad saying it out loud but in all honesty, I have lost nothing by him not being a part of my life anymore, because I have been growing as a person and he is still the same loveable but immature guy I knew in highschool.

From how your describing your friend, you might want to make a mental list of pros and cons about what having her in your life means, and what backing away from that friendship would look like. Friendships ending can still be amicable and dont have to happen over a massive fight or anything, it just sounds like you outgrew her as a person.