I guess it could be argued that if the Red Queen is this different Cinderella's step-sister that it could be that time works differently in that Enchanted Forest unlike the other Enchanted Forest. It wouldn't be the most confusing thing about the messiness of this seventh season. I mean, Ana also didn't seem to age at all during those 28 years in Wonderland. If she's not Anastasia Tremaine (She already has the exact same backstory as her), then it's really a stupid choice not to cast someone to play her when they did Lady Tremaine and Drizella. Anastasia in the Cinderella movies was well-developed, complex, and redeemed herself. Why wouldn't they include her in it when they reform villains in this show and make such complex and developed ones?

^I 100% agree.

Mostly because they already told her story. But at the same time it is kinda odd that they'd have the other two but not her. Or maybe they're planning on bringing Rigby back as some kinda surprise?

I think perhaps they're worried about backlash from Ana/Emma Rigby fans? Like why they chose not to recast Jefferson when they were originally planning to - the backlash they would've gotten from Sebastian Stan fans apparently wasn't worth including more of the Mad Hatter. I don't think the "she's a new version" line would work the same as with Alice 2.0, since Ana fans still don't have confirmation that she even was a Tremaine in the first place. I'm holding out hope that the reason they chose not to cast a new Ana is so that there's still room for Emma to maybe guest star a few episodes if she wants. Probably not gonna happen though.

Another theory I've seen going around is that Lady Tremaine killed Ana to cast the curse (based on the whole 'heart of the thing you love most' concept), which could be possible. By the end of the third movie LT certainly loved Drizella more than Ana, but that doesn't mean it has to be that way in OUAT.

They actually said that Lady Tremaine wasn't the one to cast the curse. It's basically going to be a Zelena second curse thing where you're trying to figure out how the second curse was made but the writers already said that it's not Lady Tremaine.

^ Oh, in that case nevermind. I hadn't heard that.

But it looks like they are casting an Anastasia and she'll be different from the Red Queen -- a casting call went out for her for episode 7x09. So I guess we'll find out why she hasn't been in the rest of it then.

Where did you hear about the casting call for episode 7x09?

People have posted about it on twitter and there's also a wiki page for her here: link)

Bit of an update on the Anastasia casting -- its for a tween Ana and based on link and Rebecca Ausiello saying that "regardless of how she turns out" she's happy and selfless makes me think it actually is the Red Queen.

Either way, I refuse to believe that her having the exact same backstory as Anastasia Tremaine and the same name is just a coincidence. So if she's not Anastasia Tremaine in this realm than I'm just going back to thinking she's the third Tremaine sister to the other Cinderella. And while I have quit this show because I think season 6 was the PERFECT ending for the show, I would be willing to watch that episode because of Anastasia. They just better not ruin my baby!