The Curse of Peladon
Amazonia was the Earth delegate to Peladon when it applied for membership in the Galactic Federation.
She was delayed en route, and did not arrive until after the situation of Peladon had resolved, her role having been taken on by the Third Doctor. (The Curse of Peladon)
In 3950, Amazonia was succeeded by Mavic Chen as the Guardian of the Solar System. (Legacy, Neverland)
BEHIND THE SCENES
Amazonia is never referred to by name in the on-screen dialogue, her name is given only in the closing credits.
Amazonia is also unnamed in Brian Hayles’s novelisation of the story, being referred to as simply “the lady Earth Delegate” and “Madam Chairman”.