well, if henry is right (and I think he's wrong) she's the savior so she can leave. Note, I don't mean I think he's wrong about her being the saviour, just about her bieng able to leave.

And Regina doesn't know Emma is Snow's daughter and it is my (and I think her, meaning Regina)understanding that only the fairy tale characters cant' leave, which would explain why she thought Emma could go.

But doesn't explain why she thought the twins could as they were fairy tale characters.