It's an unfortunate consequence of growing up. Even at my age, there are people that I went to high school with that never got past that point in their life. Listen to Springsteen's song "Glory Days" - it describes your situation perfectly. Some people move on and grow as individuals and learn new things and have new experiences - and others are either frightened by new things or have no desire for new things and hold on to the past.
At some point you will have to talk with her and tell her that friendship is a two way street. She has to be interested in what YOU are doing now as well as sharing her new life with you. Otherwise, you are simply a source of information about her old school

Kathleen