Look, if Monica Goodling is afraid her candid testimony will expose her to criminal prosecution, there are options. For those who missed it, her justification is here:
Attorney General Alberto R. Gonzales's senior counselor yesterday refused to testify in the Senate about her involvement in the firings of eight U.S. attorneys, invoking her Fifth Amendment right against self-incrimination.
Monica M. Goodling, who has taken an indefinite leave of absence, said in a sworn affidavit to the Senate Judiciary Committee that she will "decline to answer any and all questions" about the firings because she faces "a perilous environment in which to testify."
Perilous environments don't automatically trigger the right against self-incrimination. Frankly, the mere idea that a senior adviser to Alberto Gonzales is expressing concern that she committed a crime helps the investigation, at least temporarily.
It is possible to compel Goodling to testify by granting her immunity from prosecution based on her statements. Congress can't prosecute crimes -- it can only muck prosecutions up. See, e.g., Iran Contra.
Congress should not be deciding whether Goodling's testimony is worth immunity. That sounds like a job for a special prosecutor. You've got a senior adviser in the Department of Justice claiming that she can't testify because she might incriminate herself. Congress isn't designed to prosecute crimes. The DoJ obviously isn't the best choice to investigate itself. That only leaves an independent prosecutor to look into the matter.
I hear that Patrick Fitzgerald might be available.