Good point on Tyrion's POV. It reminds me of something I read about Jaime raping Cersei, since in the books we are seeing that scene from Jaime's perspective, which presents the act as consensual, putting the whole act in question for some readers.
I'm not saying it's a perfect analogy, just saying perception very much…

Oh, I agree. What I take from her character is not that she's irredeemable, just doomed to be what she keeps saying she is.

Of course it was a sham trial and he was gonna be found guilty, but she took the most active part in it, willingly or otherwise.
I don't think it particularly matters what influenced her testimony, any less than what influenced Pycelle's or Varys'. In the end, it was a despicable thing to betray Tyrion. Self…

Well, if it was limited to a jab, sure, but it wasn't. It was, as far as the trial went, the last nail on Tyrion's coffin. Her motivations are irrelevant when the projected outcome was confirming Tyrion's guilt.
Put in another way, she would not have been made to testify if all she would do was humiliate Tyrion.

First order of business: Pierced batnipples.

Alright. She lies on her testimony about a murder conspiracy, and she takes the opportunity to spew venom at her former lover and protector. What we don't know about the circumstances of Cersei's implied coercion or her own motivations does not balance or negate her actions.
In a way, she makes is clear herself when…