Question: Who wrote the eighteenth episode of the seventh season of "Pretty Little Liars", featuring Shay Mitchell as Emily?

Context articles: Rosewood, Pennsylvania
Mary Drake
Aeriél Miranda
Shay Mitchell
Charlotte Drake
Choose or Lose
Ravenswood (TV series)
Pretty Little Liars: The Perfectionists
List of Pretty Little Liars episodes
Pretty Little Liars (novel)

Rosewood is the fictional setting for both the "Pretty Little Liars" book series and the "Pretty Little Liars" television series.
 The fictional city is suggested to be loosely based on Rosemont, Pennsylvania.
Mary Drake is a fictional character created by I. Marlene King and portrayed by Andrea Parker in the American television series "Pretty Little Liars".
 "Pretty Little Liars" is a television adaptation of the novel series of the same name written by Sara Shepard, in which the antagonist Alison DiLaurentis has an identical twin sister, Courtney DiLaurentis.
 It is believed that Mary is the on-screen counterpart of Courtney, though her recent characterization is more in line with Alison.
 The character makes her first official introduction during the sixth-season finale "Hush, Hush, Sweet Liars".
 The Liars discover that Mary is Jessica DiLaurentis' identical twin sister, a former patient at Radley Sanitarium who is Charlotte's biological mother.
 In "The DArkest Knight", Drake is also revealed to be Spencer Hastings' biological mother.
 During "Till Death Do Us Part", the elusive A.D. is revealed to be Alex Drake, Spencer's younger identical twin sister.
 Alex believed the Liars knew who was accountable for Charlotte's murder and was also set on physically replacing Spencer due to being jealous of the life that she had.
Aeriél Christine Miranda (born April 3, 1992) is an American actress.
 She is best known for her recurring role as Shana Fring on the ABC Family series, "Pretty Little Liars" (2013–2014).
 She was first introduced as Shana on the "Pretty Little Liars" web series, "Pretty Dirty Secrets", prior to appearing on "Pretty Little Liars".
 Miranda also had a recurring role as Lana on the ABC Family series "The Nine Lives of Chloe King" (2011).
Shannon Ashley "Shay" Mitchell (born April 10, 1987) is a Canadian actress, model, entrepreneur and author.
 She is best known for her role as Emily Fields in the Freeform series "Pretty Little Liars".
Charlotte Drake is a fictional character in "Pretty Little Liars", an American mystery drama television series based on the homonymous novel series written by Sara Shepard.
 Charlotte is a character that only appears in the television series and is portrayed by Vanessa Ray.
 The character is also featured in the "Pretty Little Liars" spin-off "Pretty Dirty Secrets".
"Choose or Lose" is the eighteenth episode of the seventh season of "Pretty Little Liars", and the show's 158th episode overall, which premiered on the Freeform network in the United States on June 13, 2017.
 The episode was directed by Norman Buckley and written by Charlie Craig.
 In this episode, the Liars finally discover that Aria (Lucy Hale) has been working with 'A.D.' after Mona (Janel Parrish) investigated on Aria.
 Lieutenant Tanner (Roma Maffia) returns to Rosewood to work on the Dunhill's homicide case, quickly targeting the Liars on her radar.
 Caleb (Tyler Blackburn) and Hanna (Ashley Benson) secretly marry, while Alison (Sasha Pieterse) and Emily (Shay Mitchell) step forward with their relationship.
Ravenswood was an American supernatural teen drama, mystery-thriller television series created by I. Marlene King, Oliver Goldstick and Joseph Dougherty.
 A first spin-off of "Pretty Little Liars", ABC Family green lit the series on March 26, 2013.
 It premiered on October 22, 2013, following the "Pretty Little Liars" Halloween episode.
 The series began filming on August 21, 2013, in New Orleans, Louisiana.
Pretty Little Liars: The Perfectionists is a upcoming American teen drama television series developed by I. Marlene King, loosely based on the popular book series "The Perfectionists" written by Sara Shepard.
 A second spin-off of "Pretty Little Liars" after "Ravenswood", Freeform greenlit the series on September 25, 2017.
"Pretty Little Liars" is a TV series which premiered on ABC Family on June 8, 2010.
 Developed by I. Marlene King, the series is based on the "Pretty Little Liars" book series by Sara Shepard.
 The series follows the lives of four girls, Aria Montgomery, Hanna Marin, Emily Fields, and Spencer Hastings, whose clique falls apart after the disappearance of their leader, Alison DiLaurentis.
 One year later, the estranged friends are reunited as they begin receiving messages from a mysterious figure named "A" who threatens to expose their deepest secrets, including ones they thought only Alison knew.
Pretty Little Liars is the first book in the "Pretty Little Liars" series by Sara Shepard.
 It tells the story of four girls - Hanna, Aria, Emily and Spencer - after the disappearance of their clique leader, Alison.
 The book was written for the book packaging company Alloy Entertainment, the idea originally developed as a TV series.