According to the source, the 49-year-old reality star felt like she had no option but to leave the Bravo series after two seasons. She found the group "too toxic," the source adds of Richards' co-stars, Erika Girardi, Dorit Kemsley, Teddi Mellencamp Arroyave and Garcelle Beauvais.
Following Richards' departure, a source told ET that her exit was not a surprise to the cast.
"It's obvious she was not getting along with the women," the source said.
Throughout her seasons on the show, Richards clashed with many of the women, even choosing to skip out on two group events so she wouldn't have to film with them.
As the drama began to play out onscreen back in May, Richards told ET that she felt she was "a bit of a target" during her second season.
"There [were] a lot of issues that were brought up, and questions that I kept answering repeatedly, to where I felt I was blue in the face answering those questions, where I had nothing else to say about it and was like, 'All right, if you guys wanna keep on talking about this, I can't. There's nothing else to say,'" Richards said at the time. "I like to just resolve stuff. We can agree to disagree and move on from it. But I felt it kept going on and on and on and on and on, and enough's enough."