I’m guessing FTL 2 Zelena is the one Hansel encountered and he just THINKS our zelena is that Zelena.
That would be the easiest explanation. It just feels cobbled together, like the writers needed to give Zelena something to do besides stand around with Regina and discuss the various situations so, suddenly and inexplicably, Zelena is now also the witch from Hansel and Gretel cause “new universe”
It’s pretty awesome Lana gets to direct a Hansel and Gretel episode since she’s said that’s her favorite fairytale. Good on A&E for making that happen.