Testimony is Evidence

[SteveII]

By showing that it is objective, rather than subjective.

How might one go about that?

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I see the problem now.

1. "Witness testimony is demonstrably unreliable." You are taking all witness testimony as a whole and applying to it the fact that some testimony is unreliable. This is an excellent example of the fallacy of composition. This premise is obviously fallacious because some amount of testimony is reliable. 

She didn't say that testimony is unreliable, therefore no testimony is reliable. Her point was that testimony is unreliable, therefore you shouldn't convict someone based solely on testimony, without corroborating evidence.

Yes, that is pretty much what she said. "Witness testimony is demonstrably unreliable" as a premise must stand on its own. So is every case of witness testimony demonstrably unreliable? No, it is not. She therefore took what applies to a certain percentage and applied it to the whole as her premise. A fallacy of composition. 

But setting that aside, why do you add in "shouldn't convict someone..."?? That was not in the discussion and is only a narrow application of witness testimony of which she was not even talking about. Here are a few categories where formal testimony is weighed:

Criminal Courts (even in criminal courts, testimony is not limited to the guilt of a person. It often could be just establishing context or other facts of the matter.)
Civil Courts
Family Courts
Government Hearings
Current event reporting (news)
Historical attestations (formally writing or speaking of events that where witnessed) 

In my observation, to make this (a general discussion of witness testimony) into a "wrongful conviction" discussion is an attempt to strengthen a weak argument by appealing to people's sense of injustice rather than reasoning.