What you've described is a woman who is very insecure and uses your life as a standard by which her own success is measured. You might have hit it on the head when you said, "I feel like we're still in junior high, only worse..." And you're right, it is worse, because she has never emotionally left junior high.
Let me be frank... you can't change her and you can't make her grow up. It sounds as if you have outgrown this “friendship.” In college I became friends with someone who behaved similarly. When life was treating me well, my “friend” denounced the things that made me happy or proud of myself. If things were going poorly for me, she took the opportunity to make me feel worse. She used all of her efforts to tear me down, rather than to make herself a better person. I forgave years of this behavior from her thinking that I owed it to her out of respect for our common history. I ended the friendship when I realized that sharing a common history doesn’t mean the friendship has a future.
People grow apart, as you two apparently have. It’s not pleasant, but it’s a fact of life. You’re not guilty of anything but becoming a mature adult, and you’re not responsible for her emotional immaturity. I recommend letting this friendship fade, or at least limiting your contact with her. True friends are those who lift you up, not drag you down. Please don’t fool yourself into thinking that if you’re just more supportive, or understanding, or gracious to her that she’ll change. If your good example of friendship hasn’t made an impression on her so far, it most likely never will.