Board Thread:General Discussion/@comment-27079851-20171120082917/@comment-91424-20171121111806

Eskaver wrote: Another example could easily be that Regina chose to start a relationship with a guy whose wife she executed (as far as she knew)  and she never once told him that. Sure Zelena later said that she did it, but Regina never once during those several weeks told Robin.

That's because Regina didn't know she was the one who killed Marian. "A Tale of Two Sisters" establishes that she didn't remember the incident where Marian was incarcerated and sentenced to death. Which is why she had Sidney had to look into the past and show these events to her.