This article says the privilege can be waived by either party at any time.
https://www.legalmatch.com/law-library/article/husband-wife-privilege.html
It sounded like she wanted to refuse on the basis of the marriage, but it was ruled she couldn’t. But since she is an ex, what is the issue? Was she saying, perhaps, that the Islamic marriage overruled a state divorce? If that’s where she is, then the state rules apply.
And she may be afraid for different reasons. Maybe she should be eligible for witness protection.