Wilkinson is the lawyer who set up her own law firm last year and immediately started representing four of Hillary’s aides including Mills. Mills is also a lawyer.
Yes, I know that. But, just being a lawyer doesn't automatically mean that you have an attorney-client privilege with every person you know.
In order for Mills to claim attorney-client privilege with Clinton, she has to represent Clinton as a client. But, Mills is a State Dept. employee. Representing Clinton and being an employee of the US government at the same time, especially pertaining to US government business, appears to be a serious conflict of interest.