Everyone is different so it is hard to answer. I think a lot of the time it depends on circumstances. Could be the right guy, but the wrong time. She could have just lost the feeling in which case there is little chance it will just come back. There may be times in the future she thinks of the good times and regrets breaking it off, esp.if she ends up getting treated like dirt.
I personally try and move on as quickly as possible by deleting photos, texts, getting rid of any reminders of my ex. Obviously is it no so easy to erase things in the mind so yeh there'd be times I sit and think about the relationship. But if what I am thinking isn't in line with how I am feeling then I wouldn't go back to the relationship. It would just be fond memories and gratitude that I knew someone so lovely.
Some people are drains and some are radiators... Keep clear of the drains and hug the radiators!