Let me try another answer. Here is a quote about Empress of Outer Space (1965) by A. Bertram Chandler:
The planets of the Empire had decided on the best possible form of government for themselves: a monarchy, for quick decisions; a monarch chosen from the people, for democracy's sake; a female monarch, tall, blonde and beautiful, for dramatic appeal. Her Imperial Highness, the Empress Irene.
As I remember, the Empress had to be young, since she had to be beautiful, and back in 1965 it was hard to picture a beautiful woman much over 40. But not too young, since she had to have shown her competence - Empress Irene in particular was a former space captain, as she was over fond of reminding the officers of ships she traveled aboard.
Thus I think it was normal for an empress to be replaced - after a specific term of years, like a president, or after losing some equivalent of a vote of no confidence, like a prime minister can lose office before the end of her term - instead of serving until death.
As I remember, the empress was not elected directly by the people, as in most republics, but was selected or elected by an electoral college vaguely similar to those of the Holy Roman Empire and of the United States of America, and in the novel a member of the electoral college accompanied the empress and was authorized to veto her actions if necessary, and if she ignored the veto to call a electoral meeting to vote her out of office.
And it is possible that the planet Naboo had a similar system but the queens were usually elected at a much lower age than the space empresses in Empress of Outer Space.
Now think about the political system in medieval Japan, if it does not give too big a headache.
It is generally believed that the office of Japanese emperor evolved from a priest-king who was the chief shaman of a confederation of kings in the region of Yamato in prehistoric times. By the time of the first completely historic rulers after about 500 AD the confederation ruled most of south west Japan and the title of the supreme overlord was Okimi, or grand king.
Various Japanese rulers had been in contact with the Chinese court via tribute missions, etc. for centuries, and there was much Chinese cultural influence on Japan through Korea. So eventually the Japanese court decided to imitate the strong centralized government of China, and the Japanese ruler began to control the central government of the expanding Japanese realm. The Japanese monarchs began to call themselves Tenno, or heavenly king about 700 AD, and began to claim to be the rightful rulers of the world.
The Tenno ruled the expanding Japanese realm for centuries. Each new Tenno was usually the eldest son of the chief wife of his father, and it became the custom for a close relative of the head of the Fujiwara clan to be the chief wife of the Tenno. Whenever the Tenno was a minor, the head of the Fujiwara clan would usually be his uncle or maternal grandfather, and the logical choice to be his regent until he reached his majority. And the heads of the Fujiwara clan came to desire that the Tenno should be a minor as often as possible.
So it gradually became the custom for a new Tenno to be a child when selected by influential members of the court. Even a child could perform the ancient priestly rituals of a shaman king, while the Fujiwara regent would control the Chinese-style government in his name. After about a decade or so, as the Tenno matured, he would abdicate, and often have more power as a retired monarch and one of several powers behind the throne than when reigning.
Meanwhile new powers were growing up the newly acquired provinces of north east Japan. Groups of Samurai warriors led by powerful clans gradually usurped governmental powers in the provinces, and in 1185 established the first military government of all Japan. The rule of the Fujiwara regent acting in the name of the reigning child Tenno became limited to legalizing and approving and rubber stamping the actions of the military government and granting each new leader of it the title of shogun.
This went on during the rule of the Kamakura (1192-1333), Ashikaga (1336-1573), and Tokugawa (1603-1858) shogons. And from 1206 to 1333 the Hojo Regents ruled the shogunate in the name of child and/or powerless shoguns.
Remember that the Mongols invaded Japan in 1274 and 1281, and were defeated by local forces and the military government of the Hojo Regent Hojo Tokimune who reigned from 1268 to 1284.
Go-Uda (1267-1324) became Tenno in 1274 and abdicated in 1287. Thus he was 7 and 14 during the Mongol invasions. Suppose that in an alternate universe the Mongols were much more successful in 1281 and defeated the local forces and the forces the the Hojo regent and captured city after city. Go-Uda might have escaped from Kyoto when the Mongols captured the imperial capital and fled to join up with a military unit resisting the Mongols and more of less nominally and perhaps actually lead that unit in the fight against the Mongols.
And in an even more alternate universe there might have been a different young emperor when the Mongols invaded, possibly in different years, and he might possibly have been very precocious and led a successful resistance to the Mongols where his elders failed.
So this alternate universe historical situation would have been rather analogous to the reign of Queen Amidala of Naboo. Except that she said she was elected, and there were other young queens of Naboo later on in her life. So we might guess that the Queens of Naboo had the legal right to rule but usually just performed royal rites while older officials ruled in their names, like many child emperors of Japan.
And the child queens would be elected - by the whole population or a small group - at a young age and end their terms young enough to not try to do much ruling. And since the child queens had the legal right to rule and control the government, candidates had to be very precocious, intelligent, well educated, with a record of achievement, etc. - as well as being charming and beautiful young girls - just in case they did start controlling the government.
So perhaps the election of a Queen of Naboo might be like a junior beauty pagent, with the talent part, especially the intellectual talent part, being very important, and with the winner being crowned with the royal crown of Naboo!
So even if the Naboo were worried about relations with the Trade Federation when Amidala was elected queen, every one may have expected senior officials to handle dealing with the Trade Federation, and Amidala may have taken charge only when most of the senior officials and bureaucracy were killed or captured by Trade Federation forces during their surprise attack and invasion.