Abuse of power (unmasking names) is not always criminal, but it is impeachable, resulting in barring the culprit from public office in the future. Could also result in other penalties like the way Bill Clinton lost his law license (temporarily) when he was impeached.
Also, she may have been the leaker, which would make her a criminal who could serve prison time.
A special prosecutor is needed to cross examine her, Obama, and other senior staff members to determine who the leaker was. They must all testify under oath.
You can not impeach someone who is not holding office. That is like saying you are going to kill someone who is dead. There is no logic in the statement.