How can I get this girl I have feelings for to realize her old boyfriend doesn't care for her anymore?

Stages of Change. Romance is pretty complicated... I was about to answer the question based on prochaska's stages of change... When it occurred to me that you really were more interested in having her be attracted to you. I mean, would you be happy if she realized that and took up with someone else? Attraction is not something to turn off and on, but shared emotional experiences (scary movies?) seem to help.
Be patient+impartial. Because you have feelings for her, your suggestions may be seen as being self-serving, and thus be rejected out of hand. The steps are 1. Develop a caring, respectful, open, honest friendship with her 2. Be certain that when you are discussing him that you are very fair - make suggestions, as opposed to giving opinions. 3. Be satisfied that you were listened to -even if she does'nt agree.