Jesus, you cannot force anyone to testify against anyone.
Period.
If a person gets on the stand and states truthfully, "I decline to answer because the answer might incriminate me," that's the end of it.
Other than that, she is simply agreeing to testify truthfully, something anyone does the minute they take the stand.
It sounds like the story is nothing more than a report of what the bailiff asked her when she raised her right hand.