Spoilers for the March 6 episode. After saving Central City from a nuclear bomb and being put on bed rest, Barry doesn't have much time for coffee at Jitters. Caitlin and Harry, however, head over to the coffee shop to grab a cup when they run into the mystery waitress from Barry and Iris' wedding. That's right, the waitress returned on The Flash's "Enter Flashtime," and there's a new theory about her identity.
The mystery girl, believed by fans to be Iris and Barry's future daughter, Dawn Allen (or Dawn West-Allen, the exact name is unclear), appears in the final scene of the episode, and she literally crashes Harry and Caitlin's private coffee outing. She ran into their table, spilling her "Killer Frost" frozen drink and interrupting their conversation. "I get so clumsy when I'm nervous. I'm supposed to be meeting people here for the first time and I've got the jitters," she says. Caitlin politely listens to her babble before Harry, unsurprisingly, cuts her off and makes a hasty exit. Caitlin wishes the girl luck on her meeting, and after they leave the girl mumbles that her meeting has already gone well. So, the waitress (probably Dawn Allen), went there with the intention of meeting Caitlin and Harry, but what does this tell us about her endgame or her real identity?
The last time we saw the mystery waitress, she was in Jitters for another seemingly accidental meeting, paying for Cisco and Ralph's coffee. So, to recap, she has now met and talked to Barry, Cisco, Ralph, Caitlin, and Harry. She hasn't hurt any of them, nor has she made any super obvious references to Team Flash during their interactions. She was, however, spotted writing in the same Speed Force symbols as Barry, suggesting a deep connection and understanding of the Speed Force. Naturally, fans immediately jumped to the conclusion that she was Dawn Allen, future daughter of Barry and Iris and fellow speedster. But "Enter Flashtime" raised a new possibility: what if the mystery waitress is a speedster from another earth?
In the episode, Barry works with Jesse and Jay Garrick to stop a nuclear weapon from exploding and taking all of Central City with it. It's a very close call, one that almost defeats Barry, but eventually leads him to realize that he's fast enough to beat DeVoe. That's all well and good, but the clue about the mystery girl doesn't come until after the Flash has saved the city and everyone is going home to their Earths. While saying his goodbyes, Jay mentions that he thinks it might be time for him to retire from the hero business, pass the torch to a new speedster — a female speedster. Fans on Twitter immediately began speculating: could Jay Garrick be the one who trains this mystery girl?
If Jay is training this mystery woman, this raises another pressing question: could she still be Dawn Allen? It's possible that Dawn Allen is the daughter of Barry and Iris on another Earth, hence her fascination with Barry and Iris' wedding. This doesn't exactly explain her interest in Team Flash, but it's safe to say that it probably has something to do with the Speed Force and Barry's time there. Alternatively, if this is a Dawn Allen that this Barry and Iris end up having, then why is she being trained by a speedster on another Earth? Finally, if Jay is training this mystery girl, is it possible she's not Dawn Allen at all?
Something tells me that the answer will be far more complicated and mind bending than any current fan theories, but for now we'll just have to wait and see.