A mysterious speedster (Jessica Parker Kennedy) has been lurking in Central City throughout The Flash this season, and even though we've only seen her a handful of times, she's dropped a pretty important clue each time she's appeared.

Some fans have speculated that she's Barry (Grant Gustin) and Iris' (Candice Patton) daughter from the future, while others think she's the unborn child Cecille (Danielle Nicolet) and Joe (Jesse L. Martin) are currently expecting. Some theories even predict she'll be the unnamed female apprentice Jay Garrick (John Wesley Shipp) mentioned he was training to take over for him as The Flash on Earth 3.

To help you make sense of all these theories — and the clues that back them up — let's break down each of the Mystery Girl's appearances.

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The West-Allen Wedding.

The first appearance of this Mystery Girl was actually in the Supergirl episode of the four-way crossover, "Crisis on Earth-X." She showed up at Barry and Iris' wedding as a waiter to reassure the nervous groom before he took his vows. She seemed particularly jittery when meeting Barry, emphasizing a little too hard that she was no one special. Uh, huh. Sure, girl.

This scene is where most of the "Barry and Iris' daughter" theories come from, since she seemed way too jazzed to be at their wedding. And if you were a super-powered time traveler, wouldn't your own parents' wedding totally be on your time travel bucket list?

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Speed Force Code

Her next appearance was a few episodes later in Jitters, where she paid for Ralph (Hartley Sawyer) and Cisco's (Carlos Valdes) coffees while babbling about paying it forward. Once again, she made sure to point out that she was a total stranger, but the real kicker in this one was that she ended up writing in a journal in the cryptic Speed Force code that even the team found too difficult to crack.

This clue lends a lot of credence to the theory that Mystery Girl is a time traveler, since the Speed Force is often tied to time traveling speedsters. Not to mention, Barry wrote several odd messages in this code in the Season 4 premiere, almost all of which have turned out to be future lines of dialogue from the show. Hmmm, the plot thickens.

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Meeting Friends

Once again, Mystery Girl showed up at Jitters just in time to spill her coffee all over Caitlin (Danielle Panabaker) and Harry (Tom Cavanagh), interrupting their conversation about Killer Frost and explaining that she was nervous about meeting some people for the first time. When Caitlin told her she hoped the meeting went well, Mystery Girl forebodingly answered to herself, "It did."

Why Mystery Girl would want to derail a conversation about Killer Frost remains a mystery, but this meeting definitely felt very deliberate. The fact that she is purposefully making her way through Team Flash members indicates she knows their secret identities, which is a secret that has been pretty skillfully kept until this point.

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Joe and Cecille's Baby shower

Her final appearance was at Joe and Cecille's baby shower as a delivery girl with an anonymous gift. She creepily predicted Cecille would be due in about 21 days, before saying the gift probably came from someone who understood "time is precious" and "right now is all we've got." Hmmm, that's exactly what a time traveler would say! She disappeared around the corner just as Iris came to the door, and then she sped away in a flurry of purple and yellow lightning.

Obviously the fact that she called Cecille's due date is huge red flag that she's from the future rather than Earth 3 (it possibly even indicates that she could be Cecille and Joe's child), but the lightning is the biggest giveaway yet. Not only did it confirm she's a speedster, it also was a blend of yellow and purple lightning, which we know are the colors Barry and Iris' have when they run.

Based on that, we're sticking with the Barry and Iris' daughter theory for now, but this show has surprised us before.

The Flash finale airs Tuesday, May 22 at 8/7c on The CW.

(Full Disclosure: TV Guide is owned by CBS, of of The CW's parent company.)