Sonia's niece, Lyndah Pizarro -- who was also on the show -- tells us Sonia died Wednesday night in Arizona in her sleep.

Sonia's ex-husband, fellow "Operation Repo" star Froylan Tercero, is remembering her as "a bad ass chick that kicked some serious ass."

Froylan adds ... "She will always have a place in my heart and on my body since I still have her name tattooed on my stomach, Sonia we love you and I will honor you with all the good mementos you gave me, thank you and I love you."

While she's most known for her work on the TruTV series, Sonia also acted in movies ... including 2009's "Repo Chick" and, most recently, the 2018 flick "Followed."

Sonia's had major health issues in the past ... back in May 2018 she was hospitalized after suffering a stroke. Lyndah tells us Sonia did not die as a result of complications from the stroke.

Sonia leaves behind 3 children -- Ruby, Robert and Froylan Jr. -- as well as her grandchildren ... Bryant, Brie and Danica.

She was 60.