In the Star Wars prequels, Amidala is referred to by a few different titles which confused me a bit.

In The Phantom Menace, she is called "Queen Amidala" by many characters.

In The Attack of the Clones, she is "demoted" (it would seem) to "Senator Amidala" and she meets the current Naboo Queen, Jamailla (I think)

I've seen this issue mentioned before:

and, like the narrator in that, I was confused as well.

Does anyone know what the powers are in Naboo? Is there any canon evidence for this? It does say in the opening crawl from Attack of the Clones:

Senator Amidala, the former Queen of Naboo

which would suggest that she abdicated as that is the only way (aside death) that a monarch can stop being the monarch.