It’s often considered quite difficult to get an ex back, or win over someone who’s rejected you. I mean I never managed anything like that when I was single.
I think these mixed feelings may be part of why. 
I don’t think there’s a single easy thing you can do, but sdo try this, it;s not just self-help, in the Joe Vitale book he mentions it sometimes influencing others, especially when it’s for their own good:
Try it on your feelings, frist, hers only after you feel reasonably unconflicted towards her.