Janet van Dyne – That Stephanie Szostak plays Janet van Dyne, who will later become The Wasp, is one of the most popular theories among fans. It makes sense from the perspective that Joss Whedon has already indicated he wants to have more female Avengers. Why not introduce the character in Iron Man 3 to lay the groundwork for her becoming The Wasp in the Avengers 2? The main thing working against this theory is that Marvel Studios seems to very careful in their superhero casting. At the time that Iron Man 3 started filming, would Marvel Studios have really already made up their mind about who they wanted to play The Wasp in Avengers 2?
Wanda Maximoff – Another theory, which is not near as popular, is that Stephanie Szostak plays Wanda Maximoff, who becomes the Scarlett Witch. The main basis for this theory ties into Agent Coulson becoming the Vision. Could Stephanie Szostak be the cellist in Seattle that Agent Coulson referenced dating in the Avengers? Maybe Tony Stark goes to pay her a visit after Coulson’s death. The main thing working against this theory is that it looks like the direction Marvel is taking with Clark Gregg is making his Agent Coulson character the focus of the S.H.I.E.L.D. TV series, which would seem to indicate it would be unlikely for him to turn into the Vision in Avengers 2.
Abigail Brand – In the comic books, Abigail Brand is the commanding officer of S.W.O.R.D., which is an offshoot of S.H.I.E.L.D. that deals with extraterrestrial threats. The theory of why Stephanie Szostak could be Abigail Brand mainly revolves around that it would be a nice tie-in to the deep space suit armor and the Guardians of the Galaxy. Also, Abigail Brand was co-created by Joss Whedon, which has to have its benefits in regards to being included in Marvel Studios movies. However, Abigail Brand has green hair in the comic books, so she looks way different than Stephanie Szostak looks in the movie. Of course, Abigail Brand has been portrayed without green hair on an Iron Man animated series, so it's always a possibility.
Bethany Cabe – While not everyone will recognize the name Bethany Cabe, she is a former girlfriend of Tony Stark, who is an expert in hand-to-hand combat. The fact that Stephanie Szostak’s character appears like she is about to kiss Tony Stark in the Iron Man 3 trailer would suggest she is someone romantically linked to Tony Stark. At one point, it was rumored that Bethany Cabe would be part of Iron Man 2, so it’s not surprising that she would be showing up now. We can’t really think of a reason that Stephanie Szostak’s character wouldn’t be Bethany Cabe, so it’s the most believable rumor out there.
Early on most claiming to be in the know were pointing the finger at Janet Van Dyne, which is the name we've most often heard. However, the tide seems to be turning toward Bethany Cabe. If the newest rumors are to be believed, someone claiming inside info has confirmed that Stephanie Szostak is indeed Bethany Cabe. Even though we're hoping Stephanie Szostak is Janet van Dyne, we're starting to think the Bethany Cabe rumor has the most credibility.
Iron Man 3 is set to open in movie theaters in the United States on May 3, 2013.