Question: The actress and singer Heather Morris is best known for her role in which series, becoming a regular character in the second season?

Context:
Rory Flanagan
Rory Flanagan is a recurring fictional character from the Fox musical comedy-drama series "Glee".
 The character is portrayed by actor Damian McGinty, and appeared in "Glee" starting with its third season episode "Pot o' Gold", first broadcast on November 1, 2011.
 Rory is an exchange student from Ireland who arrives as a sophomore, and is living at the home of Brittany Pierce (Heather Morris) while studying at McKinley High.
 He joins the McKinley glee club, New Directions, in his first episode.
A Very Glee Christmas
"A Very Glee Christmas" is the tenth episode of the second season of the American musical television series "Glee", and the thirty-second episode overall.
 It was written by series co-creator Ian Brennan, directed by Alfonso Gomez-Rejon, and premiered on Fox on December 7, 2010.
 It served as the mid-season finale of season two—nearly two months elapsed before the next episode was aired—and featured Artie (Kevin McHale) trying to keep his girlfriend Brittany's (Heather Morris) belief in Santa Claus intact, and Sue (Jane Lynch) rigging the faculty Secret Santa gift exchange so she gets all the gifts, though she later becomes a Grinch when the gifts are repossessed.
Santana Lopez
Santana Lopez is a fictional character from the Fox musical comedy-drama series "Glee".
 The character is portrayed by actress Naya Rivera, and has appeared in "Glee" from its pilot episode, first broadcast on May 19, 2009.
 Santana was developed by "Glee" creators Ryan Murphy, Brad Falchuk and Ian Brennan.
 Introduced as a minor antagonist and a sidekick to Quinn Fabray (Dianna Agron) in first episode of "Glee", Santana's role grew over the course of the show's first season.
 In the second season, Rivera was promoted to series regular, and Santana was given more high-profile storylines, such as the development of her romantic feelings for her best friend Brittany Pierce (Heather Morris), and subsequent realization that she is a lesbian.
 Rivera, who has been vocally supportive of the love story between her and Morris' character, has received widespread praise for her portrayal of Santana, as well as for her for vocal work in numerous songs performed as part of the show's central glee club, New Directions.
Sexy (Glee)
"Sexy" is the fifteenth episode of the second season of the American musical comedy-drama television series "Glee", and the thirty-seventh episode overall.
 It was written by Brad Falchuk, directed by Ryan Murphy, and first aired on the Fox network on March 8, 2011.
 The episode mainly revolves around the topics of sex and adolescent sexuality.
 In it, Holly Holliday (Gwyneth Paltrow) returns to McKinley High School as a substitute teacher in a class devoted to sex education.
 Glee club director Will Schuester (Matthew Morrison) begins to develop feelings for Holly, and guidance counselor and celibacy club advisor Emma Pillsbury (Jayma Mays) is less than pleased with Holly's lessons.
 Santana (Naya Rivera) expresses her love for Brittany (Heather Morris), and Burt Hummel (Mike O'Malley) has a talk with his son Kurt (Chris Colfer) about sex.
Brittany Pierce
Brittany Susan Pierce is a fictional character from the Fox musical comedy-drama series "Glee".
 The character is portrayed by actress Heather Morris, and first appeared in the show's second episode, "Showmance".
 Brittany was developed by "Glee" creators Ryan Murphy, Brad Falchuk, and Ian Brennan.
 In "Glee", Brittany is a cheerleader, or "Cheerio" for the fictional William McKinley High School, and a member of the school's glee club led by Will Schuester.
 Morris was originally hired to teach Beyoncé's "Single Ladies" dance to the "Glee" cast.
 The show at the time was looking for a third cheerleader, and Morris landed the role.
 Morris was upgraded to a series regular in the series' second season, in which Brittany is given a larger storyline, solos and dance routines to perform.
Crazy Eyes (character)
Suzanne "Crazy Eyes" Warren is a fictional character played by Uzo Aduba on the Netflix series "Orange Is the New Black".
 Warren is portrayed as intelligent, but lacking in social skills, and prone to spiral into emotional outbursts when agitated.
 The character is the only role that has received Emmy Award recognition both in the comedy and drama genres from the same show and only the second character to earn Emmy recognition in both genres.
 Aduba won the Emmy Award for Outstanding Guest Actress in a Comedy Series as well as the Critics' Choice Television Award for Best Guest Performer in a Comedy Series for her season one performance.
 She received the Emmy Award for Outstanding Supporting Actress in a Drama Series as well as the Screen Actors Guild Award for Outstanding Performance by a Female Actor in a Comedy Series for her season two performance.
 Her season three performance again won Screen Actors Guild Award for Outstanding Performance by a Female Actor in a Comedy Series.
 She is a recurring character in season one and a regular character beginning with season two.
CSI: NY (season 2)
The second season of "" originally aired on CBS between September 2005 and May 2006.
 It consisted of 24 episodes.
 Its regular time slot continued on Wednesdays at 10pm/9c.
 The season introduced a new regular character, Lindsay Monroe, after regular Aiden Burn was fired.
 Vanessa Ferlito, who played Burn, wanted to leave the series to pursue her film career.
Heather Morris
Heather Elizabeth Morris (born February 1, 1987) is an American actress, dancer, singer and model, known for her role as Brittany S. Pierce in the Fox musical comedy-drama series "Glee".
Britney/Brittany
"Britney/Brittany" is the second episode of the second season of the American television series "Glee", and the twenty-fourth episode overall.
 Written and directed by series creator Ryan Murphy, it premiered on the Fox network on September 28, 2010, and pays tribute to Britney Spears.
 Glee club member Brittany S. Pierce (Heather Morris) experiences an anesthesia-induced hallucination in which she recreates iconic Spears moments, and comes to self-realization, and several club members follow suit.
 Co-captains Rachel (Lea Michele) and Finn (Cory Monteith) experience difficulties in their relationship, and club director Will Schuester (Matthew Morrison) becomes jealous of guidance counselor Emma Pillsbury's (Jayma Mays) new boyfriend, Dr. Carl Howell (John Stamos).
Born This Way (Glee)
"Born This Way" is the eighteenth episode of the second season of the American television series "Glee", and the fortieth episode overall.
 It originally aired on Fox in the United States on April 26, 2011.
 The episode was written by Brad Falchuk and directed by Alfonso Gomez-Rejon, and is a tribute to Lady Gaga, the second such tribute to the artist in the show's history; the first one was "Theatricality".
 Most of the major plots of the episode center on the topic of homosexuality, as Kurt (Chris Colfer) lays the groundwork for his longtime bully Dave Karofsky (Max Adler) to come to terms with his sexuality, and Santana (Naya Rivera) plots to run for school prom queen in the hopes of winning her love interest Brittany (Heather Morris) from Artie (Kevin McHale).

Answer: Glee