You are mistaken.
She was appointed Assistant to the President and Staff Secretary on January 20, 2001. As Staff Secretary, Ms. Miers acted as "the ultimate gatekeeper for what crosses the desk of the nation's commander in chief." In addition to this important role, Ms. Miers supervised more than 60 employees in four departments.
In 2003, Ms. Miers was named Assistant to the President and Deputy Chief of Staff. As part of the Office of the Chief of Staff, she was a top domestic policy advisor to the President.
Ms. Miers has served as Counsel to the President since February 2005. In this role, she has served as the top lawyer to the President and the White House, and in particular has been the principal advisor judicial nominations.
Possibly (it's been known to happen).
Perhaps I would have been better served by saying that she was **an** advisor on Judicial nominations since 2001, and promoted to **principal** advisor (i.e. White House Counsel) on judicial nominations in Feburary of this year.