Spoilers for the May 1 episode of The Flash. As Season 4 hurtles towards its finale, The Flash is finally starting to deliver answers on one of the biggest mysteries of the season: who is the mystery girl who popped up at Barry and Iris' wedding only to make a few more strange appearances at Jitters? Well, in "Therefore She Is," the mystery girl (Jessica Parker Kennedy) made another appearance, and this time it's raised a brand new theory as to her identity: could the waitress be Joe and Cecile's daughter on The Flash? Many fans have long theorized that the waitress form Barry and Iris' wedding is their daughter, Dawn, who is a speedster in the comics. But what if she's someone else's daughter?
In the final scene of "Therefore She Is," all members of Team Flash gathered at Barry and Iris' apartment to celebrate a baby shower for Joe and Cecile. After a tough week fighting Devoe (and losing), everyone is a bit demoralized, especially Cisco, who broke up with Gypsy and is sticking around in Central City. In the chaos of all the celebration and brooding, there's a knock on the door, and Cecile answers to find the mystery waitress. She tells Cecile that she's a delivery girl, just dropping off a diaper bag gift. All this seems pretty inconsequential, until she tells Cecile that she looks like she's do "21 days from tonight." That is some very specific knowledge there, mystery girl. Then she says this: "It looks like it's a gift from someone who wanted you both to know how special you are. Someone who understands that time is precious and now is all we've got." Needless to say, this entire interaction with Joe and Cecile, made some fans think that maybe the mystery girl is their daughter, not Barry and Iris'.
There definitely seems to be a connection between the waitress and Cecile, and the scene sparked a whole new theory about the mystery girl's identity. However, what happens after also seems to confirm the other theory that she is Dawn West Allen, Barry and Iris' daughter. When Iris sees commotion at the door, she goes over to Joe and Cecile to see the diaper bag, but when they turn back to the hall, the mystery girl is gone. She seems genuinely freaked out at the thought of seeing Iris, and then she speeds off, confirming that she is, in fact, a speedster. Not only is the mystery girl a speedster, she also has yellow and purple lightning — yellow being Barry's color and purple being Iris' when she got his speedster powers.
As the season finale looms, as well as Cecile's due date, fans now have two pretty solid theories as to the waitress' identity: is she Dawn Allen, or is she Joe and Cecile's daughter? The truth is, she could be either. Neither Joe nor Cecile have meta DNA, and Cecile's mind-reading powers were confirmed to have nothing to do with the baby when they first appeared, suggesting that the child itself is not a meta. That said, neither Wally nor Barry were born metas. It's possible that Cecile will give birth to a perfectly ordinary baby girl who will later grow up to become a speedster. And it would be kind of fun for The Flash to throw fans for a loop after the theory that the mystery girl was Dawn Allen gained so much momentum.
On the other hand, the fact that the waitress is a speedster and that her colors are a mix of both Barry's and Iris' does seem like pretty strong evidence that she's at least related to both of them, something Joe and Cecile's baby will not be (by blood, at least). Her hesitancy to meet Iris also raises a few questions. Mystery girl has met pretty much everyone on Team Flash except for Iris, and she runs away from her when she has the chance — why? Does something happen to Iris that only the mystery girl knows about? What is their connection, and why is it so important?
Fans have been assured that we will find out the identity of the mystery girl/waitress on The Flash before the end of the season, so luckily we won't have to wait too long to find out.