Sorry. She doesn’t get to be an active part of the defense team in the original trial and then claim that her religious ‘faith’ won’t allow her to get on the witness stand and give honest answers to a few questions about whether the defendant had a vigorous defense.
I think she does. The defense was a public event in the courtroom, with a complete transcript retained. Her testimony has no unique value for this phase of the case. It takes an exceptional situation to override a constitutional right, and that burden is not met in this case. I don't see a conflict between actively working in court to prevent an execution and refusing to testify in the same court on the quality of the defense, not when that testimony would aid in deciding for the death penalty.