They can't force her to testify if it would incriminate herself. That isn't what is happening here. If she has been offered immunity then she can't incriminate

They can't force her to testify if it would incriminate herself. That isn't what is happening here. If she has been offered immunity then she can't incriminate herself. Also answering questions regarding an offense she has already been convicted of isn't incriminating herself. If during her testimony she believes that answering a specific question would incriminate herself she can refuse to answer it upon that basis. What she can't legally do is refuse to answer any questions whatsoever.