I loved their dynamic in this episode. I'm still not entirely convinced that Zelena was telling the truth, maybe she isn't Regina's sister. I know there's 99% chance that she is, but why did she need Regina's blood? Maybe to get into Cora's crypt because she's not really related to Regina.
Anyway, she probably is her half-sister and I don't dislike it as much as I thought I would (if she's Cora's firstborn, that means all kinds of plot holes and retcons). But I loved their scenes and I can't wait to see what Zelena's planning to do and why. She said that she wants to take everything from Regina because she got everything Zelena wanted, but this can't be all.
It's kind of funny that Zelena is so envious of Regina who had such a crappy life.
Zelena wants everything Regina never wanted.