How to Get Away with Murder wouldn't be the same show if there weren't a handful of new questions at the end of each episode. Season 5 has enough mysteries without Bonnie’s sister playing a part, but according to Annalise such a sister exists — and I have a feeling viewers are about to get to know her in an important flashback. So who plays Bonnie’s sister on HTGAWM? There are a few different actresses who could have been chosen for the role at this point.
The IMDB page for HTGAWM doesn't have anyone listed as Bonnie’s sister or with the last name Winterbottom, but the official synopsis for Thursday’s episode, "It’s Her Kid," features an actress named Elizabeth Morton who will guest star as Julie Winterbottom. There are a couple of actresses with that name, but a HTGAWM fan account on Twitter posted who they believe the correct one is and she does bear a resemblance to BonBon. If it is the correct actress, then she’s been out of the game for a couple of years. The last movie she appeared in was actually a short called The Burning and that was in 2016. But HTGAWM isn’t known for casting big A-list celebrities for minor roles, so it could very well be her.
Another actress who might be brought on to play Bonnie’s sister is also named Elizabeth Morton. She, too, hasn’t been in many big TV shows or movies in recent years, but she had a small role in ABC’s short-lived series 666 Park Avenue. Since HTGAWM is on the same network, she could be the Elizabeth Morton the episode synopsis was referring to. Since neither actress has the show listed on their respective IMDB accounts right now, it's hard to say for certain. But both women could pass for Bonnie’s sister on HTGAWM and since there hasn't been an official announcement about who plays her, it could really be either of them.
The synopsis for Episode 6, "We Can Find him," features Morton’s name again, but also a child actor by the name of Violet Hicks as Skyler Winterbottom. This brings up a whole other mystery of whether or not Bonnie’s sister has a kid in present day or the big mystery about Bonnie’s missing baby is a red herring to throw off viewers. Right now, viewers are being led to believe that Nate discovered that Gabriel is Bonnie’s long lost son, thought to be dead, but who was really stolen from the hospital. But in reality, this little girl could be Bonnie’s baby from a past pregnancy that hasn't been revealed yet. I know, my head hurts just from considering all of that too. It should be noted, by the way, that IMDB has been tricked before.
After the reveal about Bonnie’s sister, fans on Twitter and Reddit alike were thrown into a tizzy with theories that Bonnie has a twin. While it’s true that she could be revealed to be one half of a pair of twins and Liza Weil could play a dual role this season, it looks like one of the Morton actresses will be Julie, her sister, who may or may not have stolen her infant years ago. This is broaching on soap opera territory at this point, but I’m kind of here for it. Again, this is all just fan speculation.
It would be a lot easier if IMDB was updated to reflect the official ABC episode synopsis since there’s more than one actress with the name. But either way, the show has introduced Bonnie’s sister to the mix and thus added another level to the double helix of intertwining storylines this season.