The New York Times On Judy,

Link

.....Her decision to testify came after she obtained what she described as a waiver offered "voluntarily and personally" by a source who said she was no longer bound by any pledge of confidentiality she had made to him. She said the source had made clear that he genuinely wanted her to testify.

She could have obtained this waiver without every having gone to jail, so why now.....four weeks before getting out?

To keep from being indicted for criminal contempt.