The CW's The Flash might be on winter hiatus right now, but that break in new episodes only means more time for fans to try to solve one of the more curious mysteries of the show's fourth season -- namely who was the random girl at Barry Allen (Grant Gustin) and Iris West's (Candice Patton) wedding?
As you might recall from the first hour of "Crisis on Earth-X," a waitress (played by Jessica Parker Kennedy) was serving sparkling water ahead of the ceremony. The mystery girl -- who fans noted looked like an oddly perfect version of what a combination of Barry and Iris' genetics might look like -- was incredibly excited to be at the wedding and rambled on to Barry about it so much that it prompted him to ask if he knew her. She dismissed the notion, but did remind Barry to say, "I do."
While Barry never actually did say "I do" -- which might cause trouble for the West-Allens -- fans have pretty much decided that the mystery girl wasn't just a really enthusiastic waitress and is, instead, somehow related to Barry and Iris. While some have looked at the evidence and decided that the mystery girl has to be Dawn Allen, the couple's daughter, it's also very likely that she's their granddaughter, Jenni Ognats, and the clues for that lie in another Arrowverse show, Supergirl.
On Supergirl this season, Mon-El (Chris Wood) returned to National City after having been sent out into space by Supergirl/Kara Danvers (Melissa Benoist) to save his life. The catch here is that Mon-El didn't just do a fly-by of the solar system then come back. Instead, he was sucked into the future and ended up in the 31st century. While there, he formed the Legion of Super-Heroes. While on a mission, the Legion ended up traveling back in time, ultimately finding themselves in National City in the 21st century.
Why this is significant in proving that the mystery girl is Jenni Ognats and not Dawn Allen is two-fold. First, the mystery girl appears in the Supergirl hour of the "Crisis on Earth-X" event, and while that may not mean much generally, if you consider that Jenni is herself a Legionnaire in comics, it makes a little more sense that Jenni would show up in an appearance connected directly to the series where the rest of the team is. But more about Jenni as a member of the Legion of Super-Heroes. In comics, Jenni goes by the code name XS, and during the Legion's first trip to the 20th century, XS was separated from the rest of the team. She ended up interacting with people who were, functionally, her ancestors. Jenni specifically became friends with her cousin, Bart Allen.
With the Legion of Super-Heroes being introduced to the Arrowverse on Supergirl and with not all of the team members being introduced on that show just yet -- after all, there were multiple pods on the ship and we've only met Mon-El and Imra Ardeen going into the midseason premiere -- it would make sense that there are going to be more Legionnaires showing up. Adding in the comic book element that XS was somehow separated from her team when the ventured into the past would open the door for a somewhat easy explanation as to why Jenni was on Earth-1 instead of Earth-38, the corner of the multiverse Supergirl lives on.
With the heavy focus on the Legion of Super-Heroes this season, it seems unlikely that The Flash would miss an opportunity to use that as an opportunity to further complicate Barry Allen's story, especially since when the show returns in January it will jump right into a storyline from comics that also has ties to the 30th century -- "The Trial of The Flash".
The Flash returns from midseason hiatus on January 16, 2018.