Sounds far more like something Corso would say, as Count_Mario suggested. Taking into account Risha's background, I'd doubt she'd say anything of the sort.
Also, how do people know it was a companion?
Answer: Nobody said they know it was a companion. We're just guessing. And having been through the all 8 class storylines twice now along with all the other missions, my best guess was Risha.
Retraction: However, after searching my memory banks, I have recalled the correct answer. And no, that doesn't mean I searched it. I remember it now.
Answer: The one who said it was Kalyo.
Statement: It stuck in my mind, though the reason is silly, because she mentions backstabbing, and that's what the Operative's skill is, Back-stab.