Born Padmé Naberrie, Queen Amidala was the formal name of the royal leader of Naboo.
When in danger, Queen Amidala disguised herself as one of her handmaidens, and adopted her less formal name of Padmé.
When her terms ended, Amidala was constitutionally obligated to step down as Queen... At the request of the new Naboo monarch, Queen Jamillia, Amidala served as Senator of Naboo, taking the position once occupied by Palpatine.
Before slipping away, Padmé remained strong enough to give birth. In the strange alien facility of Anakin's nightmares, she gave birth to twins -- Leia and Luke Skywalker. Obi-Wan Kenobi, Yoda, and Bail Organa vowed to keep the children safe.