If she had refused to appear after having been subpoenaed then I think that could have been done.But having appeared I think it could only be done if she had been granted immunity and *still* refused to cooperate.
Um they will have a very clear idea what she will testify to BEFORE granting immunity. If she doesnt she will have a clear understanding she will be sitting in a federal pen while her buddies are talking about her at cocktail parties. She will roll over, she is not that strong. She has F ed up big time and my bet is she flips far sooner than others think. Then it will all begin to roll like the stone in Raides of the Lost Ark, but everyone on the hill will be diving out of the way.