She played the recurring character of Jackie Robbins in medical drama series "ER". Alexander has made a number of guest appearances on other television shows, including "", "NYPD Blue", "Third Watch", "Cosby", "Better off Ted", "La Femme Nikita", and "Body of Proof". In 2000, Alexander won critical acclaim for her performance as Fran Boyd, a mother addicted to drugs in the Emmy Award-winning HBO miniseries "The Corner". She later appeared in the films "Emmett's Mark" and "Dark Blue", and starred opposite Rob Lowe in the Lifetime television movie "Perfect Strangers". In 2002 through 2008, she portrayed the character of Alexx Woods, a medical examiner in the CBS police drama "". Alexander left "CSI: Miami" shortly before the end of the 2007–2008 season. Her final appearance aired on May 5, 2008. On February 2, 2009, she returned to the role of Alexx Woods for a guest appearance in the episode "". She returned again as Alexx Woods in guest appearances in the episodes "Out of Time" on September 21, 2009 and "" on October 19, 2009. In fall 2008, Alexander was cast as a lead character in the HBO drama pilot "Treme", that premiered on April 11, 2010. She played a bar owner in a neighborhood of New Orleans affected by Hurricane Katrina. She received critical acclaim for her performance in the show. Alexander starred in the award-winning HBO television series by David Simon from 2010 to 2013. The series ended after four seasons. She later was cast in Shonda Rhimes's drama series "Scandal" as Kerry Washington's character's mother. In 2015, she was nominated for a Primetime Emmy Award for Outstanding Guest Actress in a Drama Series for her performance. In 2014, Alexander was cast as older sister of Queen Latifah's title character in the HBO Film "Bessie" about iconic blues singer Bessie Smith. She was nominated for a Critics' Choice Television Award for Best Supporting Actress in a Movie/Miniseries.