SHE prevents it. It (open court) does not prevent it. The onus is on her to take the opportunity given to her by law to testify and if she executes her right to decline, so be it. People do that in court all the time--execute their right to testify or not testify. And those may be DP cases, too, but it doesn't matter--every defendant has the right to testify, or not.
I must say, though, what I have bolded tells me a lot about why you want to continue to argue this. I will leave this argument now, with this: Your opinion is valid and is one held by many citizens including many here on WS. I agree with much of what you say, just not all of it. And that, my friend, has to be my final word on this because I have posted on this subject several times now and to continue posting on it would be in violation of WS TOS.