If Zelena is trying to time travel, one of the laws of magic is that you can't change the past. What I thought was interesting is how they never tried to do this, not even in Wonderland. I think that Zelena can only change the past with her curse in ways its already been changed, or she is predetermined to change certain things in the past which causes the current timeline. Look at the twister. It is green, very similar to Zelena's magic. Therefore, I think that Zelena goes back in time, fails with her original plan, and ends up creating the twister which sends the baby version of herself to Oz. Thoughts?