Read this slowly…
FORMER Secretaries of State are NOT referred to as [FORMER] Dignitaries. They are called FOREIGN dignitaries and FORMER Secretaries of State.
The only reason for a FORMER Secretary of State to be referred to as a [FORMER] Dignitary is if she's no longer a Dignitary.
The only way for her to no longer be a Dignitary of the United States is if she had her citizenship removed…either voluntarily or not.
If not voluntary, then there are only a couple reasons a person could lose their US citizenship…and one of them starts with "T".