Brewer grew up loving all forms of the arts, especially movies and theater productions. She started by taking theater classes in 1999 at a College for Kids class during her middle school years. She performed in dramas, musicals, comedies, and many improvisations during her theater training at Dionysus Theater. Brewer appeared and spoke in PSAs for the Super Bowl of Caring Houston Food Drive in Houston, Texas for two consecutive years which aired on NBC, ABC, and CBS. Brewer continues her stage training through The Groundlings Theater and School.
In 2011, Brewer made her television debut as Adelaide "Addie" Langdon in American Horror Story: Murder House. "I first got word of the audition for the show from a friend of mine." She said. "They were looking for a young lady with Down syndrome who could act. My headshot and resume were submitted and I was called for an audition and, to my surprise I got the part. I was so excited." About her role, Brewer stated: "Adelaide is a complex character, but the most difficult part of playing Adelaide is learning how to portray someone who isn’t always viewed acceptable to her mother and society. This is a new challenge for me."
After the show's first season ended, she appeared on Southland in an episode titled "Heat", which aired on February 20, 2013. Also in 2013, she returned to American Horror Story for the third season, subtitled Coven, playing the supporting role of Nan, a young witch who is clairvoyant.
It was announced at the 2014 PaleyFest that Brewer would return to the series for the fourth season, subtitled American Horror Story: Freak Show. Although, at a later date, show creator Ryan Murphy indicated Brewer may not appear during the season. Brewer was later confirmed after appearing in a promo for the final two episodes. She both voiced and played Marjorie, the ventriloquist dummy / alternate personality of another character.
In February 2015, Brewer became the first woman with Down syndrome to walk the red carpet at New York Fashion Week, which she did for designer Carrie Hammer. Talking about the experience, Brewer said, "It's amazing that the fashion industry are including individuals with disabilities," she said. "It's an amazing opportunity for women, women that are disabled." During Another time she also said,"Young girls and even young women [see me] and say 'hey, if she can do it so can I'. It's a true inspiration being a role model for any young women to [encourage them] in being who they are and showing who they are."
In July 2015, she appeared as a character named Jamie in three episodes of the popular web series Raymond & Lane. While In September, Brewer appeared on Switched at Birth in an episode titled "Between hope and fear".
Brewer was the first model with Down Syndrome to walk the New York Fashion Week catwalk.