True, but just like 'every single US tax-filer signs away his Fifth Amendment rights every April 15th', once waived, that Right cannot be taken back or retroactively affected.
Lerner could either testify or not, but she has no legal right to take the stand to state her innocence THEN plead the fifth - once on the stand, she was obligated to answer.
Arrest her for contempt of court and toss her in a dark, rat infested hole.
;-)