A lot happened in the massive CW Supergirl x Arrow x Flash x Legends of Tomorrow four-way crossover, but no reveal in "Crisis on Earth-X" was more crucial to The Flash than the mysterious young woman who talks to Barry right before his wedding, prompting the question: is the waitress from "Crisis on Earth-X" Barry and Iris' daughter? Dawn Allen might have made her Flash debut in the crossover, and, though her appearance was short, it raises a lot of questions.
In the first part of "Crisis on Earth-X," a young woman approaches Barry in the church before his wedding. She offers him water to calm his nerves, and then proceeds to babble about how she is definitely a complete and total stranger to Barry (sure). She also reminds him to say "I Do" and tells him how happy she is to get to see their wedding. That's the extent of their interaction, but for any Flash fan, it's obvious that this mysterious waitress is more than she seems. Based on her look and her palpable excitement at seeing Barry and Iris wed (not to mention her Barry Allen awkwardness), most fans immediately reached the same conclusion: this is Dawn Allen, Barry and Iris' future daughter. But, why was she there? And what happened to her after the Nazis invaded?
Assuming this waitress is Dawn Allen, her short scene in "Crisis on Earth-X" left fans with a weird feeling and loads of questions. In the comics, Dawn Allen inherited some of Barry's powers, which could explain how Barry could meet his adult daughter at his own wedding. (Let the record show that the lessons of Flashpoint have not been passed down to future generations.) Unfortunately, the Dawn Allen of the comics also never met her father. She and her twin brother, Don (yes, Iris named her children Dawn and Don) were born after their father died. If this holds true for The Flash, then Dawn's appearance at the wedding could signal the beginning of the end for Barry Allen.
If Dawn Allen is from the future, and in her future Barry is dead, then why would she travel back to the marriage that got interrupted by Nazis from another Earth? You'd think future Iris would tell her kids about how her wedding was ruined by an evil army from another Earth. Dawn could be from another Earth entirely. She also disappeared entirely from "Crisis on Earth-X" after the wedding was attacked. Was she hurt in the Earth-X Nazi invasion? Or did she speed back to her time? Did something happen at the wedding that erased her existence? All of these questions were left open, and it's unclear if The Flash plans on answering any of them in the near future.
"Crisis on Earth-X" didn't confirm the Dawn Allen theory, but the crossover was full of allusions to pregnancy. There was Felicity telling Iris she was "glowing" and plenty of talk of babies and commitment and future children. Could Iris already be pregnant? If she is, and if Dawn Allen is the same Dawn from the comics (aka the one who never met her father), then this could mean terrible things for Barry. Put simply, it would mean he only has 9 or so months to live. It looks like the Thinker might be a greater foe than we originally thought.
Dawn Allen mystery aside, it definitely looks like Barry and Iris are on the road to parenthood. And they might not be the only ones. The Arrowverse now has two relatively stable superhero couples — Barry and Iris and Felicity and Oliver — which means fans could be getting superheroes on daddy duty sooner rather than later.