Last seen in Thor: The Dark World, grad student Darcy has risen up in the world in the decade that's passed since then! Now an astrophysicist with a doctorate, Darcy is one of four elite scientists (in wildly differing fields) who are brought in by S.W.O.R.D. to try to figure out what's happening in Westview.
Darcy is the one who figures out that there's a signal emanating from the bubble — a mix of cosmic/magical energy and what turns out to be a broadcast signal — and sets up a way to "watch" the "episodes." Another fan theory gets proven true: she's the person watching TV at the end of the first episode, watching and taking notes in front of a TV.