I could be mistaken - she may have been granted transactional immunity, not use immunity. It’s been so long, I can’t remember anymore.
Remind me what she needed immunity for. Is it illegal for a young White House intern to accept an invitation from the President of the United States to come into the Oval Office and give him a blow job? Offhand I can’t think of anything she’s known to have done that any prosecuting authority would even dream of pressing charges for.