She's selfish for stringting you along so I'd hardly think that she's wasting energy by being mad at you, she's likely not thinking too much about you if she's still got exes in the picture that she's re-doing either.
If she chooses you after the ex and her break up again, afterall exes are exes for a good reason which I'm sure neither one of them have worked on themeselves to fix) then you are'nt likely going to last very long again either. You're too easy for her.
Don't let her back in (even as a friend) just leave it at zero contact so that you can get over her and her need to maintain exes in her life to recycle when convenient. There are way better women out there then someone like her. Heal and start looking for one and leave her in the past where she belongs.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion