we have an official answer to Regina’s smirk in the vault from A&E’s interview to TVGuide:
What should we divine from that smirk on Regina’s face after she locked up Zelena’s pendant in her vault?
Kitsis: It’s funny that you bring that up. That’s one of my favorite scenes in that episode and maybe the series. What that smirk said was: I won and I like myself today. She used light magic. She went against somebody she didn’t think she could beat. She has Robin Hood (Sean Maguire) and she is making huge strides toward a new life. We wanted to show you a private moment where Regina — who really cast the curse because she felt like she could never win and never find happiness — in that moment alone, she smiles and says, “I won.”
Some fans worried that it meant she might’ve been conspiring with Rumple.
Kitsis: No, that was a genuine moment. It’s hard when you have a show like this because we love to give surprises and twists, but sometimes people read into our genuine moments. Really, she won and she’s happy. Let’s enjoy that for her.