This isn't Parris's first episode, but it's the first one where she's basically the protagonist of the whole episode — and going by her real name, rather than her "Geraldine" alter ego. After waking up from having been snapped out of existence by Thanos, she learns that five years have passed and that her mother, Maria, died of cancer in the interim.
She returns to work at S.W.O.R.D., where, after being sent to investigate an apparent missing persons case, she discovers the strange mystery of Westview and gets sucked into (and eventually kicked out of) its sitcom bubble. At that point, she reveals what she's learned, or at least what she's pretty sure: Wanda's in control of it all.