In response to several people on Twitter, Ms. Barr claimed she did not know Ms. Jarrett was African-American. “I thought she was Saudi,” she said to one supporter. To others, she tweeted that she believed Ms. Jarrett was “Jewish and Persian.”

At 12:37 a.m., Ms. Barr replied to a tweet from the account @therealcornett, which falsely claimed that Channing Dungey, the president of ABC Entertainment, had consulted with “an enraged” Michelle Obama before deciding to cancel “Roseanne.”

“Is this true?” Ms. Barr wrote.

She went on to retweet a clip of an interview with the 2012 Republican presidential candidate Herman Cain that had been originally posted by the Fox Business host Trish Regan. “I believe they were looking for a reason to cancel Roseanne and here’s why,” Mr. Cain said in the clip. “Even though the show was a ratings success, forces within ABC didn’t like the fact that her conservative defense of certain things was so popular.”

She also retweeted a post by Jack Posobiec — a right-wing commentator who promoted the “Pizzagate” hoax — that included a photograph of the comedian George Carlin with the caption, “This man wouldn’t last a day on Twitter.”

In another self-serving retweet, Ms. Barr posted words of encouragement from the right-wing British commentator Katie Hopkins, who lost her job last year at the radio station LBC after tweeting that a “final solution” was needed to combat terrorism. “I have found the more I am fired, the busier I become,” Ms. Hopkins wrote. “You are headed for greatness.”

Ms. Barr also reacted to “Roseanne” cast members. In response to Michael Fishman, who played Ms. Barr’s son on the show and posted a statement condemning Ms. Barr’s tweet, she responded at 5 a.m., “You throw me under the bus. Nice!”