I have this friend who's always calling up her other friends when I'm over or e-mailing them or whatever

My best friend and I have been friends for almost 20 years. We both turn 30 this year. The best advice I can give, is be honest with her. Tell her how you feel, and that it is disrespectful not only to you but to your relationship with her as well. If she gets all rude about it, and is like "whatever", then maybe you should reavulate your friendship with her. A true friend will listen, be respectful and be considerate to ones feelings.