No matter what you do, there is always a possibility that she goes back. you cant control her.
Be with her as much as you can, but if she seems resistant, dont push. Otherwise you are prolly making the same mistakes as her ex. Dont be needy. Show her a good time, amp up the emotions when you do hang out together.
If she says: yeah, but i cant hang out with you, because my ex wants me back, dont push, but do make her realize what she is doing. Ask her if she really wants to get back to him as there must have been a reason she broke up.
if she says: i cnat hang out because i am too stressed out, say: ok, i understand, but on the other hand, we would probably have a good time and relaxation is the best medicine for stress. (something llike that, dont matter if it is cheesy. it should make her think).
You see, like that you wouldnt be really pushing. It doesnt provide certitude about the outcome, but unless you chain her to the bed, you cant really control her actions.
cheers and good luck!
"Stop being a fucking vagina and escalate" - CaptainJackHarkness
Like the naked leads the blind.
I know I'm selfish, I'm unkind.
Sucker love I always find,
Someone to bruise and leave behind.
placebo - every me, every you