EXCLUSIVE

Mariah Carey's former assistant has just fired back at the singer's blackmail allegation with her own lawsuit, claiming she was the victim of horrible abuse by one of Mariah's key people, and the singer did nothing about it.

Lianna Azarian claims in a new lawsuit, Mariah's former manager, Stella Bulochnikov committed various acts of abuse, including slapping her butt and breasts, urinating on her, tackling her to the ground and sitting on her. Azarian also claims Stella called her the n-word, and a "f***ing Armenian whore."

According to the lawsuit, Azarian says Stella ridiculed her breasts, "including placing objects under her breasts such as iPhones, television remote controls and utensils."

Azarian claims a lot of the alleged abuse occurred in Mariah's presence and she did nothing.

Azarian also says Mariah committed acts of physical, emotional and psychological abuse against her.

TMZ broke the story ... Mariah sued Azarian, claiming she secretly videotaped embarrassing and intimate activities and then blackmailed after Mariah fired her ... saying if she didn't get $8 million she'd release the videos.

Azarian is suing Mariah, Stella and others.

We reached out to Stella and are waiting for a comment. And, we reached out to Mariah's folks ... so far, no word back.